RCU pull request for v5.19

This pull request contains the following branches:
 
 docs.2022.04.20a: Documentation updates.
 
 fixes.2022.04.20a: Miscellaneous fixes.
 
 nocb.2022.04.11b: Callback-offloading updates, mainly simplifications.
 
 rcu-tasks.2022.04.11b: RCU-tasks updates, including some -rt fixups,
 	handling of systems with sparse CPU numbering, and a fix for a
 	boot-time race-condition failure.
 
 srcu.2022.05.03a: Put SRCU on a memory diet in order to reduce the size
 	of the srcu_struct structure.
 
 torture.2022.04.11b: Torture-test updates fixing some bugs in tests and
 	closing some testing holes.
 
 torture-tasks.2022.04.20a: Torture-test updates for the RCU tasks flavors,
 	most notably ensuring that building rcutorture and friends does
 	not change the RCU-tasks-related Kconfig options.
 
 torturescript.2022.04.20a: Torture-test scripting updates.
 
 exp.2022.05.11a: Expedited grace-period updates, most notably providing
 	milliseconds-scale (not all that) soft real-time response from
 	synchronize_rcu_expedited().  This is also the first time in
 	almost 30 years of RCU that someone other than me has pushed
 	for a reduction in the RCU CPU stall-warning timeout, in this
 	case by more than three orders of magnitude from 21 seconds to
 	20 milliseconds.  This tighter timeout applies only to expedited
 	grace periods.
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Merge tag 'rcu.2022.05.19a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

Pull RCU update from Paul McKenney:

 - Documentation updates

 - Miscellaneous fixes

 - Callback-offloading updates, mainly simplifications

 - RCU-tasks updates, including some -rt fixups, handling of systems
   with sparse CPU numbering, and a fix for a boot-time race-condition
   failure

 - Put SRCU on a memory diet in order to reduce the size of the
   srcu_struct structure

 - Torture-test updates fixing some bugs in tests and closing some
   testing holes

 - Torture-test updates for the RCU tasks flavors, most notably ensuring
   that building rcutorture and friends does not change the
   RCU-tasks-related Kconfig options

 - Torture-test scripting updates

 - Expedited grace-period updates, most notably providing
   milliseconds-scale (not all that) soft real-time response from
   synchronize_rcu_expedited().

   This is also the first time in almost 30 years of RCU that someone
   other than me has pushed for a reduction in the RCU CPU stall-warning
   timeout, in this case by more than three orders of magnitude from 21
   seconds to 20 milliseconds. This tighter timeout applies only to
   expedited grace periods

* tag 'rcu.2022.05.19a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (80 commits)
  rcu: Move expedited grace period (GP) work to RT kthread_worker
  rcu: Introduce CONFIG_RCU_EXP_CPU_STALL_TIMEOUT
  srcu: Drop needless initialization of sdp in srcu_gp_start()
  srcu: Prevent expedited GPs and blocking readers from consuming CPU
  srcu: Add contention check to call_srcu() srcu_data ->lock acquisition
  srcu: Automatically determine size-transition strategy at boot
  rcutorture: Make torture.sh allow for --kasan
  rcutorture: Make torture.sh refscale and rcuscale specify Tasks Trace RCU
  rcutorture: Make kvm.sh allow more memory for --kasan runs
  torture: Save "make allmodconfig" .config file
  scftorture: Remove extraneous "scf" from per_version_boot_params
  rcutorture: Adjust scenarios' Kconfig options for CONFIG_PREEMPT_DYNAMIC
  torture: Enable CSD-lock stall reports for scftorture
  torture: Skip vmlinux check for kvm-again.sh runs
  scftorture: Adjust for TASKS_RCU Kconfig option being selected
  rcuscale: Allow rcuscale without RCU Tasks Rude/Trace
  rcuscale: Allow rcuscale without RCU Tasks
  refscale: Allow refscale without RCU Tasks Rude/Trace
  refscale: Allow refscale without RCU Tasks
  rcutorture: Allow specifying per-scenario stat_interval
  ...

Documentation/RCU/Design/Data-Structures/Data-Structures.rst

@@ -973,7 +973,7 @@ The ``->dynticks`` field counts the corresponding CPU's transitions to
 and from either dyntick-idle or user mode, so that this counter has an
 even value when the CPU is in dyntick-idle mode or user mode and an odd
 value otherwise. The transitions to/from user mode need to be counted
-for user mode adaptive-ticks support (see timers/NO_HZ.txt).
+for user mode adaptive-ticks support (see Documentation/timers/no_hz.rst).
 
 The ``->rcu_need_heavy_qs`` field is used to record the fact that the
 RCU core code would really like to see a quiescent state from the

Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.rst

@@ -406,7 +406,7 @@ In earlier implementations, the task requesting the expedited grace
 period also drove it to completion. This straightforward approach had
 the disadvantage of needing to account for POSIX signals sent to user
 tasks, so more recent implemementations use the Linux kernel's
-`workqueues <https://www.kernel.org/doc/Documentation/core-api/workqueue.rst>`__.
+workqueues (see Documentation/core-api/workqueue.rst).
 
 The requesting task still does counter snapshotting and funnel-lock
 processing, but the task reaching the top of the funnel lock does a

Documentation/RCU/Design/Requirements/Requirements.rst

@@ -370,8 +370,8 @@ pointer fetched by rcu_dereference() may not be used outside of the
 outermost RCU read-side critical section containing that
 rcu_dereference(), unless protection of the corresponding data
 element has been passed from RCU to some other synchronization
-mechanism, most commonly locking or `reference
+mechanism, most commonly locking or reference counting
-counting <https://www.kernel.org/doc/Documentation/RCU/rcuref.txt>`__.
+(see ../../rcuref.rst).
 
 .. |high-quality implementation of C11 memory_order_consume [PDF]| replace:: high-quality implementation of C11 ``memory_order_consume`` [PDF]
 .. _high-quality implementation of C11 memory_order_consume [PDF]: http://www.rdrop.com/users/paulmck/RCU/consume.2015.07.13a.pdf
@@ -2654,6 +2654,38 @@ synchronize_rcu(), and rcu_barrier(), respectively. In
 three APIs are therefore implemented by separate functions that check
 for voluntary context switches.
 
+Tasks Rude RCU
+~~~~~~~~~~~~~~
+
+Some forms of tracing need to wait for all preemption-disabled regions
+of code running on any online CPU, including those executed when RCU is
+not watching.  This means that synchronize_rcu() is insufficient, and
+Tasks Rude RCU must be used instead.  This flavor of RCU does its work by
+forcing a workqueue to be scheduled on each online CPU, hence the "Rude"
+moniker.  And this operation is considered to be quite rude by real-time
+workloads that don't want their ``nohz_full`` CPUs receiving IPIs and
+by battery-powered systems that don't want their idle CPUs to be awakened.
+
+The tasks-rude-RCU API is also reader-marking-free and thus quite compact,
+consisting of call_rcu_tasks_rude(), synchronize_rcu_tasks_rude(),
+and rcu_barrier_tasks_rude().
+
+Tasks Trace RCU
+~~~~~~~~~~~~~~~
+
+Some forms of tracing need to sleep in readers, but cannot tolerate
+SRCU's read-side overhead, which includes a full memory barrier in both
+srcu_read_lock() and srcu_read_unlock().  This need is handled by a
+Tasks Trace RCU that uses scheduler locking and IPIs to synchronize with
+readers.  Real-time systems that cannot tolerate IPIs may build their
+kernels with ``CONFIG_TASKS_TRACE_RCU_READ_MB=y``, which avoids the IPIs at
+the expense of adding full memory barriers to the read-side primitives.
+
+The tasks-trace-RCU API is also reasonably compact,
+consisting of rcu_read_lock_trace(), rcu_read_unlock_trace(),
+rcu_read_lock_trace_held(), call_rcu_tasks_trace(),
+synchronize_rcu_tasks_trace(), and rcu_barrier_tasks_trace().
+
 Possible Future Changes
 -----------------------
 

Documentation/RCU/arrayRCU.rst

@@ -33,8 +33,8 @@ Situation 1: Hash Tables
 
 Hash tables are often implemented as an array, where each array entry
 has a linked-list hash chain.  Each hash chain can be protected by RCU
-as described in the listRCU.txt document.  This approach also applies
+as described in listRCU.rst.  This approach also applies to other
-to other array-of-list situations, such as radix trees.
+array-of-list situations, such as radix trees.
 
 .. _static_arrays:
 

Documentation/RCU/checklist.rst

@@ -140,8 +140,7 @@ over a rather long period of time, but improvements are always welcome!
 		prevents destructive compiler optimizations.  However,
 		with a bit of devious creativity, it is possible to
 		mishandle the return value from rcu_dereference().
-		Please see rcu_dereference.txt in this directory for
+		Please see rcu_dereference.rst for more information.
-		more information.
 
 		The rcu_dereference() primitive is used by the
 		various "_rcu()" list-traversal primitives, such
@@ -151,7 +150,7 @@ over a rather long period of time, but improvements are always welcome!
 		primitives.  This is particularly useful in code that
 		is common to readers and updaters.  However, lockdep
 		will complain if you access rcu_dereference() outside
-		of an RCU read-side critical section.  See lockdep.txt
+		of an RCU read-side critical section.  See lockdep.rst
 		to learn what to do about this.
 
 		Of course, neither rcu_dereference() nor the "_rcu()"
@@ -323,7 +322,7 @@ over a rather long period of time, but improvements are always welcome!
 	primitives when the update-side lock is held is that doing so
 	can be quite helpful in reducing code bloat when common code is
 	shared between readers and updaters.  Additional primitives
-	are provided for this case, as discussed in lockdep.txt.
+	are provided for this case, as discussed in lockdep.rst.
 
 	One exception to this rule is when data is only ever added to
 	the linked data structure, and is never removed during any
@@ -480,4 +479,4 @@ over a rather long period of time, but improvements are always welcome!
 	both rcu_barrier() and synchronize_rcu(), if necessary, using
 	something like workqueues to to execute them concurrently.
 
-	See rcubarrier.txt for more information.
+	See rcubarrier.rst for more information.

Documentation/RCU/rcu.rst

@@ -10,9 +10,8 @@ A "grace period" must elapse between the two parts, and this grace period
 must be long enough that any readers accessing the item being deleted have
 since dropped their references.  For example, an RCU-protected deletion
 from a linked list would first remove the item from the list, wait for
-a grace period to elapse, then free the element.  See the
+a grace period to elapse, then free the element.  See listRCU.rst for more
-:ref:`Documentation/RCU/listRCU.rst <list_rcu_doc>` for more information on
+information on using RCU with linked lists.
-using RCU with linked lists.
 
 Frequently Asked Questions
 --------------------------
@@ -50,7 +49,7 @@ Frequently Asked Questions
 - If I am running on a uniprocessor kernel, which can only do one
   thing at a time, why should I wait for a grace period?
 
-  See :ref:`Documentation/RCU/UP.rst <up_doc>` for more information.
+  See UP.rst for more information.
 
 - How can I see where RCU is currently used in the Linux kernel?
 
@@ -64,13 +63,13 @@ Frequently Asked Questions
 
 - What guidelines should I follow when writing code that uses RCU?
 
-  See the checklist.txt file in this directory.
+  See checklist.rst.
 
 - Why the name "RCU"?
 
   "RCU" stands for "read-copy update".
-  :ref:`Documentation/RCU/listRCU.rst <list_rcu_doc>` has more information on where
+  listRCU.rst has more information on where this name came from, search
-  this name came from, search for "read-copy update" to find it.
+  for "read-copy update" to find it.
 
 - I hear that RCU is patented?  What is with that?
 

Documentation/RCU/rculist_nulls.rst

@@ -8,7 +8,7 @@ This section describes how to use hlist_nulls to
 protect read-mostly linked lists and
 objects using SLAB_TYPESAFE_BY_RCU allocations.
 
-Please read the basics in Documentation/RCU/listRCU.rst
+Please read the basics in listRCU.rst.
 
 Using 'nulls'
 =============

Documentation/RCU/stallwarn.rst

@@ -162,6 +162,26 @@ CONFIG_RCU_CPU_STALL_TIMEOUT
 	Stall-warning messages may be enabled and disabled completely via
 	/sys/module/rcupdate/parameters/rcu_cpu_stall_suppress.
 
+CONFIG_RCU_EXP_CPU_STALL_TIMEOUT
+--------------------------------
+
+	Same as the CONFIG_RCU_CPU_STALL_TIMEOUT parameter but only for
+	the expedited grace period. This parameter defines the period
+	of time that RCU will wait from the beginning of an expedited
+	grace period until it issues an RCU CPU stall warning. This time
+	period is normally 20 milliseconds on Android devices.	A zero
+	value causes the CONFIG_RCU_CPU_STALL_TIMEOUT value to be used,
+	after conversion to milliseconds.
+
+	This configuration parameter may be changed at runtime via the
+	/sys/module/rcupdate/parameters/rcu_exp_cpu_stall_timeout, however
+	this parameter is checked only at the beginning of a cycle. If you
+	are in a current stall cycle, setting it to a new value will change
+	the timeout for the -next- stall.
+
+	Stall-warning messages may be enabled and disabled completely via
+	/sys/module/rcupdate/parameters/rcu_cpu_stall_suppress.
+
 RCU_STALL_DELAY_DELTA
 ---------------------
 

Documentation/RCU/whatisRCU.rst

@@ -224,7 +224,7 @@ synchronize_rcu()
 	be delayed.  This property results in system resilience in face
 	of denial-of-service attacks.  Code using call_rcu() should limit
 	update rate in order to gain this same sort of resilience.  See
-	checklist.txt for some approaches to limiting the update rate.
+	checklist.rst for some approaches to limiting the update rate.
 
 rcu_assign_pointer()
 ^^^^^^^^^^^^^^^^^^^^
@@ -318,7 +318,7 @@ rcu_dereference()
 	must prohibit.	The rcu_dereference_protected() variant takes
 	a lockdep expression to indicate which locks must be acquired
 	by the caller. If the indicated protection is not provided,
-	a lockdep splat is emitted.  See Documentation/RCU/Design/Requirements/Requirements.rst
+	a lockdep splat is emitted.  See Design/Requirements/Requirements.rst
 	and the API's code comments for more details and example usage.
 
 .. 	[2] If the list_for_each_entry_rcu() instance might be used by
@@ -399,8 +399,7 @@ for specialized uses, but are relatively uncommon.
 
 This section shows a simple use of the core RCU API to protect a
 global pointer to a dynamically allocated structure.  More-typical
-uses of RCU may be found in :ref:`listRCU.rst <list_rcu_doc>`,
+uses of RCU may be found in listRCU.rst, arrayRCU.rst, and NMI-RCU.rst.
-:ref:`arrayRCU.rst <array_rcu_doc>`, and :ref:`NMI-RCU.rst <NMI_rcu_doc>`.
 ::
 
 	struct foo {
@@ -482,10 +481,9 @@ So, to sum up:
 	RCU read-side critical sections that might be referencing that
 	data item.
 
-See checklist.txt for additional rules to follow when using RCU.
+See checklist.rst for additional rules to follow when using RCU.
-And again, more-typical uses of RCU may be found in :ref:`listRCU.rst
+And again, more-typical uses of RCU may be found in listRCU.rst,
-<list_rcu_doc>`, :ref:`arrayRCU.rst <array_rcu_doc>`, and :ref:`NMI-RCU.rst
+arrayRCU.rst, and NMI-RCU.rst.
-<NMI_rcu_doc>`.
 
 .. _4_whatisRCU:
 
@@ -579,7 +577,7 @@ to avoid having to write your own callback::
 
 	kfree_rcu(old_fp, rcu);
 
-Again, see checklist.txt for additional rules governing the use of RCU.
+Again, see checklist.rst for additional rules governing the use of RCU.
 
 .. _5_whatisRCU:
 
@@ -663,7 +661,7 @@ been able to write-acquire the lock otherwise.  The smp_mb__after_spinlock()
 promotes synchronize_rcu() to a full memory barrier in compliance with
 the "Memory-Barrier Guarantees" listed in:
 
-	Documentation/RCU/Design/Requirements/Requirements.rst
+	Design/Requirements/Requirements.rst
 
 It is possible to nest rcu_read_lock(), since reader-writer locks may
 be recursively acquired.  Note also that rcu_read_lock() is immune

Documentation/admin-guide/kernel-parameters.txt

@@ -4893,6 +4893,18 @@
 
 	rcupdate.rcu_cpu_stall_timeout= [KNL]
 			Set timeout for RCU CPU stall warning messages.
+			The value is in seconds and the maximum allowed
+			value is 300 seconds.
+
+	rcupdate.rcu_exp_cpu_stall_timeout= [KNL]
+			Set timeout for expedited RCU CPU stall warning
+			messages.  The value is in milliseconds
+			and the maximum allowed value is 21000
+			milliseconds. Please note that this value is
+			adjusted to an arch timer tick resolution.
+			Setting this to zero causes the value from
+			rcupdate.rcu_cpu_stall_timeout to be used (after
+			conversion from seconds to milliseconds).
 
 	rcupdate.rcu_expedited= [KNL]
 			Use expedited grace-period primitives, for
@@ -4955,10 +4967,34 @@
 			number avoids disturbing real-time workloads,
 			but lengthens grace periods.
 
+	rcupdate.rcu_task_stall_info= [KNL]
+			Set initial timeout in jiffies for RCU task stall
+			informational messages, which give some indication
+			of the problem for those not patient enough to
+			wait for ten minutes.  Informational messages are
+			only printed prior to the stall-warning message
+			for a given grace period. Disable with a value
+			less than or equal to zero.  Defaults to ten
+			seconds.  A change in value does not take effect
+			until the beginning of the next grace period.
+
+	rcupdate.rcu_task_stall_info_mult= [KNL]
+			Multiplier for time interval between successive
+			RCU task stall informational messages for a given
+			RCU tasks grace period.  This value is clamped
+			to one through ten, inclusive.	It defaults to
+			the value three, so that the first informational
+			message is printed 10 seconds into the grace
+			period, the second at 40 seconds, the third at
+			160 seconds, and then the stall warning at 600
+			seconds would prevent a fourth at 640 seconds.
+
 	rcupdate.rcu_task_stall_timeout= [KNL]
-			Set timeout in jiffies for RCU task stall warning
+			Set timeout in jiffies for RCU task stall
-			messages.  Disable with a value less than or equal
+			warning messages.  Disable with a value less
-			to zero.
+			than or equal to zero.	Defaults to ten minutes.
+			A change in value does not take effect until
+			the beginning of the next grace period.
 
 	rcupdate.rcu_self_test= [KNL]
 			Run the RCU early boot self tests
@@ -5377,6 +5413,17 @@
 	smart2=		[HW]
 			Format: <io1>[,<io2>[,...,<io8>]]
 
+	smp.csd_lock_timeout= [KNL]
+			Specify the period of time in milliseconds
+			that smp_call_function() and friends will wait
+			for a CPU to release the CSD lock.  This is
+			useful when diagnosing bugs involving CPUs
+			disabling interrupts for extended periods
+			of time.  Defaults to 5,000 milliseconds, and
+			setting a value of zero disables this feature.
+			This feature may be more efficiently disabled
+			using the csdlock_debug- kernel parameter.
+
 	smsc-ircc2.nopnp	[HW] Don't use PNP to discover SMC devices
 	smsc-ircc2.ircc_cfg=	[HW] Device configuration I/O port
 	smsc-ircc2.ircc_sir=	[HW] SIR base I/O port
@@ -5608,6 +5655,30 @@
 			off:    Disable mitigation and remove
 				performance impact to RDRAND and RDSEED
 
+	srcutree.big_cpu_lim [KNL]
+			Specifies the number of CPUs constituting a
+			large system, such that srcu_struct structures
+			should immediately allocate an srcu_node array.
+			This kernel-boot parameter defaults to 128,
+			but takes effect only when the low-order four
+			bits of srcutree.convert_to_big is equal to 3
+			(decide at boot).
+
+	srcutree.convert_to_big [KNL]
+			Specifies under what conditions an SRCU tree
+			srcu_struct structure will be converted to big
+			form, that is, with an rcu_node tree:
+
+				   0:  Never.
+				   1:  At init_srcu_struct() time.
+				   2:  When rcutorture decides to.
+				   3:  Decide at boot time (default).
+				0x1X:  Above plus if high contention.
+
+			Either way, the srcu_node tree will be sized based
+			on the actual runtime number of CPUs (nr_cpu_ids)
+			instead of the compile-time CONFIG_NR_CPUS.
+
 	srcutree.counter_wrap_check [KNL]
 			Specifies how frequently to check for
 			grace-period sequence counter wrap for the
@@ -5625,6 +5696,14 @@
 			expediting.  Set to zero to disable automatic
 			expediting.
 
+	srcutree.small_contention_lim [KNL]
+			Specifies the number of update-side contention
+			events per jiffy will be tolerated before
+			initiating a conversion of an srcu_struct
+			structure to big form.	Note that the value of
+			srcutree.convert_to_big must have the 0x10 bit
+			set for contention-based conversions to occur.
+
 	ssbd=		[ARM64,HW]
 			Speculative Store Bypass Disable control
 

arch/Kconfig

@@ -35,6 +35,7 @@ config KPROBES
 	depends on MODULES
 	depends on HAVE_KPROBES
 	select KALLSYMS
+	select TASKS_RCU if PREEMPTION
 	help
 	  Kprobes allows you to trap at almost any kernel address and
 	  execute a callback function.  register_kprobe() establishes

include/linux/rcupdate.h

@@ -196,6 +196,7 @@ void synchronize_rcu_tasks_rude(void);
 void exit_tasks_rcu_start(void);
 void exit_tasks_rcu_finish(void);
 #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
+#define rcu_tasks_classic_qs(t, preempt) do { } while (0)
 #define rcu_tasks_qs(t, preempt) do { } while (0)
 #define rcu_note_voluntary_context_switch(t) do { } while (0)
 #define call_rcu_tasks call_rcu

include/linux/sched.h

@@ -2118,6 +2118,47 @@ static inline void cond_resched_rcu(void)
 #endif
 }
 
+#ifdef CONFIG_PREEMPT_DYNAMIC
+
+extern bool preempt_model_none(void);
+extern bool preempt_model_voluntary(void);
+extern bool preempt_model_full(void);
+
+#else
+
+static inline bool preempt_model_none(void)
+{
+	return IS_ENABLED(CONFIG_PREEMPT_NONE);
+}
+static inline bool preempt_model_voluntary(void)
+{
+	return IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY);
+}
+static inline bool preempt_model_full(void)
+{
+	return IS_ENABLED(CONFIG_PREEMPT);
+}
+
+#endif
+
+static inline bool preempt_model_rt(void)
+{
+	return IS_ENABLED(CONFIG_PREEMPT_RT);
+}
+
+/*
+ * Does the preemption model allow non-cooperative preemption?
+ *
+ * For !CONFIG_PREEMPT_DYNAMIC kernels this is an exact match with
+ * CONFIG_PREEMPTION; for CONFIG_PREEMPT_DYNAMIC this doesn't work as the
+ * kernel is *built* with CONFIG_PREEMPTION=y but may run with e.g. the
+ * PREEMPT_NONE model.
+ */
+static inline bool preempt_model_preemptible(void)
+{
+	return preempt_model_full() || preempt_model_rt();
+}
+
 /*
  * Does a critical section need to be broken due to another
  * task waiting?: (technically does not depend on CONFIG_PREEMPTION,

include/linux/srcutree.h

@@ -47,11 +47,9 @@ struct srcu_data {
  */
 struct srcu_node {
 	spinlock_t __private lock;
-	unsigned long srcu_have_cbs[4];		/* GP seq for children */
+	unsigned long srcu_have_cbs[4];		/* GP seq for children having CBs, but only */
-						/*  having CBs, but only */
+						/*  if greater than ->srcu_gq_seq. */
-						/*  is > ->srcu_gq_seq. */
+	unsigned long srcu_data_have_cbs[4];	/* Which srcu_data structs have CBs for given GP? */
-	unsigned long srcu_data_have_cbs[4];	/* Which srcu_data structs */
-						/*  have CBs for given GP? */
 	unsigned long srcu_gp_seq_needed_exp;	/* Furthest future exp GP. */
 	struct srcu_node *srcu_parent;		/* Next up in tree. */
 	int grplo;				/* Least CPU for node. */
@@ -62,18 +60,24 @@ struct srcu_node {
  * Per-SRCU-domain structure, similar in function to rcu_state.
  */
 struct srcu_struct {
-	struct srcu_node node[NUM_RCU_NODES];	/* Combining tree. */
+	struct srcu_node *node;			/* Combining tree. */
 	struct srcu_node *level[RCU_NUM_LVLS + 1];
 						/* First node at each level. */
+	int srcu_size_state;			/* Small-to-big transition state. */
 	struct mutex srcu_cb_mutex;		/* Serialize CB preparation. */
-	spinlock_t __private lock;		/* Protect counters */
+	spinlock_t __private lock;		/* Protect counters and size state. */
 	struct mutex srcu_gp_mutex;		/* Serialize GP work. */
 	unsigned int srcu_idx;			/* Current rdr array element. */
 	unsigned long srcu_gp_seq;		/* Grace-period seq #. */
 	unsigned long srcu_gp_seq_needed;	/* Latest gp_seq needed. */
 	unsigned long srcu_gp_seq_needed_exp;	/* Furthest future exp GP. */
+	unsigned long srcu_gp_start;		/* Last GP start timestamp (jiffies) */
 	unsigned long srcu_last_gp_end;		/* Last GP end timestamp (ns) */
+	unsigned long srcu_size_jiffies;	/* Current contention-measurement interval. */
+	unsigned long srcu_n_lock_retries;	/* Contention events in current interval. */
+	unsigned long srcu_n_exp_nodelay;	/* # expedited no-delays in current GP phase. */
 	struct srcu_data __percpu *sda;		/* Per-CPU srcu_data array. */
+	bool sda_is_static;			/* May ->sda be passed to free_percpu()? */
 	unsigned long srcu_barrier_seq;		/* srcu_barrier seq #. */
 	struct mutex srcu_barrier_mutex;	/* Serialize barrier ops. */
 	struct completion srcu_barrier_completion;
@@ -81,10 +85,23 @@ struct srcu_struct {
 	atomic_t srcu_barrier_cpu_cnt;		/* # CPUs not yet posting a */
 						/*  callback for the barrier */
 						/*  operation. */
+	unsigned long reschedule_jiffies;
+	unsigned long reschedule_count;
 	struct delayed_work work;
 	struct lockdep_map dep_map;
 };
 
+/* Values for size state variable (->srcu_size_state). */
+#define SRCU_SIZE_SMALL		0
+#define SRCU_SIZE_ALLOC		1
+#define SRCU_SIZE_WAIT_BARRIER	2
+#define SRCU_SIZE_WAIT_CALL	3
+#define SRCU_SIZE_WAIT_CBS1	4
+#define SRCU_SIZE_WAIT_CBS2	5
+#define SRCU_SIZE_WAIT_CBS3	6
+#define SRCU_SIZE_WAIT_CBS4	7
+#define SRCU_SIZE_BIG		8
+
 /* Values for state variable (bottom bits of ->srcu_gp_seq). */
 #define SRCU_STATE_IDLE		0
 #define SRCU_STATE_SCAN1	1
@@ -121,6 +138,7 @@ struct srcu_struct {
 #ifdef MODULE
 # define __DEFINE_SRCU(name, is_static)					\
 	is_static struct srcu_struct name;				\
+	extern struct srcu_struct * const __srcu_struct_##name;		\
 	struct srcu_struct * const __srcu_struct_##name			\
 		__section("___srcu_struct_ptrs") = &name
 #else

include/linux/torture.h

@@ -118,7 +118,7 @@ void _torture_stop_kthread(char *m, struct task_struct **tp);
 	_torture_stop_kthread("Stopping " #n " task", &(tp))
 
 #ifdef CONFIG_PREEMPTION
-#define torture_preempt_schedule() preempt_schedule()
+#define torture_preempt_schedule() __preempt_schedule()
 #else
 #define torture_preempt_schedule()	do { } while (0)
 #endif

kernel/bpf/Kconfig

@@ -27,6 +27,7 @@ config BPF_SYSCALL
 	bool "Enable bpf() system call"
 	select BPF
 	select IRQ_WORK
+	select TASKS_RCU if PREEMPTION
 	select TASKS_TRACE_RCU
 	select BINARY_PRINTF
 	select NET_SOCK_MSG if NET

kernel/rcu/Kconfig

@@ -77,31 +77,56 @@ config TASKS_RCU_GENERIC
 	  This option enables generic infrastructure code supporting
 	  task-based RCU implementations.  Not for manual selection.
 
-config TASKS_RCU
+config FORCE_TASKS_RCU
-	def_bool PREEMPTION
+	bool "Force selection of TASKS_RCU"
+	depends on RCU_EXPERT
+	select TASKS_RCU
+	default n
 	help
-	  This option enables a task-based RCU implementation that uses
+	  This option force-enables a task-based RCU implementation
-	  only voluntary context switch (not preemption!), idle, and
+	  that uses only voluntary context switch (not preemption!),
-	  user-mode execution as quiescent states.  Not for manual selection.
+	  idle, and user-mode execution as quiescent states.  Not for
+	  manual selection in most cases.
+
+config TASKS_RCU
+	bool
+	default n
+	select IRQ_WORK
+
+config FORCE_TASKS_RUDE_RCU
+	bool "Force selection of Tasks Rude RCU"
+	depends on RCU_EXPERT
+	select TASKS_RUDE_RCU
+	default n
+	help
+	  This option force-enables a task-based RCU implementation
+	  that uses only context switch (including preemption) and
+	  user-mode execution as quiescent states.  It forces IPIs and
+	  context switches on all online CPUs, including idle ones,
+	  so use with caution.	Not for manual selection in most cases.
 
 config TASKS_RUDE_RCU
-	def_bool 0
+	bool
-	help
+	default n
-	  This option enables a task-based RCU implementation that uses
-	  only context switch (including preemption) and user-mode
-	  execution as quiescent states.  It forces IPIs and context
-	  switches on all online CPUs, including idle ones, so use
-	  with caution.
-
-config TASKS_TRACE_RCU
-	def_bool 0
 	select IRQ_WORK
+
+config FORCE_TASKS_TRACE_RCU
+	bool "Force selection of Tasks Trace RCU"
+	depends on RCU_EXPERT
+	select TASKS_TRACE_RCU
+	default n
 	help
 	  This option enables a task-based RCU implementation that uses
 	  explicit rcu_read_lock_trace() read-side markers, and allows
-	  these readers to appear in the idle loop as well as on the CPU
+	  these readers to appear in the idle loop as well as on the
-	  hotplug code paths.  It can force IPIs on online CPUs, including
+	  CPU hotplug code paths.  It can force IPIs on online CPUs,
-	  idle ones, so use with caution.
+	  including idle ones, so use with caution.  Not for manual
+	  selection in most cases.
+
+config TASKS_TRACE_RCU
+	bool
+	default n
+	select IRQ_WORK
 
 config RCU_STALL_COMMON
 	def_bool TREE_RCU
@@ -195,6 +220,20 @@ config RCU_BOOST_DELAY
 
 	  Accept the default if unsure.
 
+config RCU_EXP_KTHREAD
+	bool "Perform RCU expedited work in a real-time kthread"
+	depends on RCU_BOOST && RCU_EXPERT
+	default !PREEMPT_RT && NR_CPUS <= 32
+	help
+	  Use this option to further reduce the latencies of expedited
+	  grace periods at the expense of being more disruptive.
+
+	  This option is disabled by default on PREEMPT_RT=y kernels which
+	  disable expedited grace periods after boot by unconditionally
+	  setting rcupdate.rcu_normal_after_boot=1.
+
+	  Accept the default if unsure.
+
 config RCU_NOCB_CPU
 	bool "Offload RCU callback processing from boot-selected CPUs"
 	depends on TREE_RCU
@@ -225,7 +264,7 @@ config RCU_NOCB_CPU
 
 config TASKS_TRACE_RCU_READ_MB
 	bool "Tasks Trace RCU readers use memory barriers in user and idle"
-	depends on RCU_EXPERT
+	depends on RCU_EXPERT && TASKS_TRACE_RCU
 	default PREEMPT_RT || NR_CPUS < 8
 	help
 	  Use this option to further reduce the number of IPIs sent

kernel/rcu/Kconfig.debug

@@ -28,9 +28,6 @@ config RCU_SCALE_TEST
 	depends on DEBUG_KERNEL
 	select TORTURE_TEST
 	select SRCU
-	select TASKS_RCU
-	select TASKS_RUDE_RCU
-	select TASKS_TRACE_RCU
 	default n
 	help
 	  This option provides a kernel module that runs performance
@@ -47,9 +44,6 @@ config RCU_TORTURE_TEST
 	depends on DEBUG_KERNEL
 	select TORTURE_TEST
 	select SRCU
-	select TASKS_RCU
-	select TASKS_RUDE_RCU
-	select TASKS_TRACE_RCU
 	default n
 	help
 	  This option provides a kernel module that runs torture tests
@@ -66,9 +60,6 @@ config RCU_REF_SCALE_TEST
 	depends on DEBUG_KERNEL
 	select TORTURE_TEST
 	select SRCU
-	select TASKS_RCU
-	select TASKS_RUDE_RCU
-	select TASKS_TRACE_RCU
 	default n
 	help
 	  This option provides a kernel module that runs performance tests
@@ -91,6 +82,20 @@ config RCU_CPU_STALL_TIMEOUT
 	  RCU grace period persists, additional CPU stall warnings are
 	  printed at more widely spaced intervals.
 
+config RCU_EXP_CPU_STALL_TIMEOUT
+	int "Expedited RCU CPU stall timeout in milliseconds"
+	depends on RCU_STALL_COMMON
+	range 0 21000
+	default 20 if ANDROID
+	default 0 if !ANDROID
+	help
+	  If a given expedited RCU grace period extends more than the
+	  specified number of milliseconds, a CPU stall warning is printed.
+	  If the RCU grace period persists, additional CPU stall warnings
+	  are printed at more widely spaced intervals.  A value of zero
+	  says to use the RCU_CPU_STALL_TIMEOUT value converted from
+	  seconds to milliseconds.
+
 config RCU_TRACE
 	bool "Enable tracing for RCU"
 	depends on DEBUG_KERNEL

kernel/rcu/rcu.h

@@ -210,7 +210,9 @@ static inline bool rcu_stall_is_suppressed_at_boot(void)
 extern int rcu_cpu_stall_ftrace_dump;
 extern int rcu_cpu_stall_suppress;
 extern int rcu_cpu_stall_timeout;
+extern int rcu_exp_cpu_stall_timeout;
 int rcu_jiffies_till_stall_check(void);
+int rcu_exp_jiffies_till_stall_check(void);
 
 static inline bool rcu_stall_is_suppressed(void)
 {
@@ -523,6 +525,8 @@ static inline bool rcu_check_boost_fail(unsigned long gp_state, int *cpup) { ret
 static inline void show_rcu_gp_kthreads(void) { }
 static inline int rcu_get_gp_kthreads_prio(void) { return 0; }
 static inline void rcu_fwd_progress_check(unsigned long j) { }
+static inline void rcu_gp_slow_register(atomic_t *rgssp) { }
+static inline void rcu_gp_slow_unregister(atomic_t *rgssp) { }
 #else /* #ifdef CONFIG_TINY_RCU */
 bool rcu_dynticks_zero_in_eqs(int cpu, int *vp);
 unsigned long rcu_get_gp_seq(void);
@@ -534,14 +538,19 @@ int rcu_get_gp_kthreads_prio(void);
 void rcu_fwd_progress_check(unsigned long j);
 void rcu_force_quiescent_state(void);
 extern struct workqueue_struct *rcu_gp_wq;
+#ifdef CONFIG_RCU_EXP_KTHREAD
+extern struct kthread_worker *rcu_exp_gp_kworker;
+extern struct kthread_worker *rcu_exp_par_gp_kworker;
+#else /* !CONFIG_RCU_EXP_KTHREAD */
 extern struct workqueue_struct *rcu_par_gp_wq;
+#endif /* CONFIG_RCU_EXP_KTHREAD */
+void rcu_gp_slow_register(atomic_t *rgssp);
+void rcu_gp_slow_unregister(atomic_t *rgssp);
 #endif /* #else #ifdef CONFIG_TINY_RCU */
 
 #ifdef CONFIG_RCU_NOCB_CPU
-bool rcu_is_nocb_cpu(int cpu);
 void rcu_bind_current_to_nocb(void);
 #else
-static inline bool rcu_is_nocb_cpu(int cpu) { return false; }
 static inline void rcu_bind_current_to_nocb(void) { }
 #endif
 

kernel/rcu/rcu_segcblist.c

@@ -505,10 +505,10 @@ void rcu_segcblist_advance(struct rcu_segcblist *rsclp, unsigned long seq)
 		WRITE_ONCE(rsclp->tails[j], rsclp->tails[RCU_DONE_TAIL]);
 
 	/*
-	 * Callbacks moved, so clean up the misordered ->tails[] pointers
+	 * Callbacks moved, so there might be an empty RCU_WAIT_TAIL
-	 * that now point into the middle of the list of ready-to-invoke
+	 * and a non-empty RCU_NEXT_READY_TAIL.  If so, copy the
-	 * callbacks.  The overall effect is to copy down the later pointers
+	 * RCU_NEXT_READY_TAIL segment to fill the RCU_WAIT_TAIL gap
-	 * into the gap that was created by the now-ready segments.
+	 * created by the now-ready-to-invoke segments.
 	 */
 	for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
 		if (rsclp->tails[j] == rsclp->tails[RCU_NEXT_TAIL])

kernel/rcu/rcuscale.c

@@ -268,6 +268,8 @@ static struct rcu_scale_ops srcud_ops = {
 	.name		= "srcud"
 };
 
+#ifdef CONFIG_TASKS_RCU
+
 /*
  * Definitions for RCU-tasks scalability testing.
  */
@@ -295,6 +297,16 @@ static struct rcu_scale_ops tasks_ops = {
 	.name		= "tasks"
 };
 
+#define TASKS_OPS &tasks_ops,
+
+#else // #ifdef CONFIG_TASKS_RCU
+
+#define TASKS_OPS
+
+#endif // #else // #ifdef CONFIG_TASKS_RCU
+
+#ifdef CONFIG_TASKS_TRACE_RCU
+
 /*
  * Definitions for RCU-tasks-trace scalability testing.
  */
@@ -324,6 +336,14 @@ static struct rcu_scale_ops tasks_tracing_ops = {
 	.name		= "tasks-tracing"
 };
 
+#define TASKS_TRACING_OPS &tasks_tracing_ops,
+
+#else // #ifdef CONFIG_TASKS_TRACE_RCU
+
+#define TASKS_TRACING_OPS
+
+#endif // #else // #ifdef CONFIG_TASKS_TRACE_RCU
+
 static unsigned long rcuscale_seq_diff(unsigned long new, unsigned long old)
 {
 	if (!cur_ops->gp_diff)
@@ -797,7 +817,7 @@ rcu_scale_init(void)
 	long i;
 	int firsterr = 0;
 	static struct rcu_scale_ops *scale_ops[] = {
-		&rcu_ops, &srcu_ops, &srcud_ops, &tasks_ops, &tasks_tracing_ops
+		&rcu_ops, &srcu_ops, &srcud_ops, TASKS_OPS TASKS_TRACING_OPS
 	};
 
 	if (!torture_init_begin(scale_type, verbose))

kernel/rcu/rcutorture.c

@@ -737,6 +737,50 @@ static struct rcu_torture_ops busted_srcud_ops = {
 	.name		= "busted_srcud"
 };
 
+/*
+ * Definitions for trivial CONFIG_PREEMPT=n-only torture testing.
+ * This implementation does not necessarily work well with CPU hotplug.
+ */
+
+static void synchronize_rcu_trivial(void)
+{
+	int cpu;
+
+	for_each_online_cpu(cpu) {
+		rcutorture_sched_setaffinity(current->pid, cpumask_of(cpu));
+		WARN_ON_ONCE(raw_smp_processor_id() != cpu);
+	}
+}
+
+static int rcu_torture_read_lock_trivial(void) __acquires(RCU)
+{
+	preempt_disable();
+	return 0;
+}
+
+static void rcu_torture_read_unlock_trivial(int idx) __releases(RCU)
+{
+	preempt_enable();
+}
+
+static struct rcu_torture_ops trivial_ops = {
+	.ttype		= RCU_TRIVIAL_FLAVOR,
+	.init		= rcu_sync_torture_init,
+	.readlock	= rcu_torture_read_lock_trivial,
+	.read_delay	= rcu_read_delay,  /* just reuse rcu's version. */
+	.readunlock	= rcu_torture_read_unlock_trivial,
+	.readlock_held	= torture_readlock_not_held,
+	.get_gp_seq	= rcu_no_completed,
+	.sync		= synchronize_rcu_trivial,
+	.exp_sync	= synchronize_rcu_trivial,
+	.fqs		= NULL,
+	.stats		= NULL,
+	.irq_capable	= 1,
+	.name		= "trivial"
+};
+
+#ifdef CONFIG_TASKS_RCU
+
 /*
  * Definitions for RCU-tasks torture testing.
  */
@@ -780,47 +824,16 @@ static struct rcu_torture_ops tasks_ops = {
 	.name		= "tasks"
 };
 
-/*
+#define TASKS_OPS &tasks_ops,
- * Definitions for trivial CONFIG_PREEMPT=n-only torture testing.
- * This implementation does not necessarily work well with CPU hotplug.
- */
 
-static void synchronize_rcu_trivial(void)
+#else // #ifdef CONFIG_TASKS_RCU
-{
-	int cpu;
 
-	for_each_online_cpu(cpu) {
+#define TASKS_OPS
-		rcutorture_sched_setaffinity(current->pid, cpumask_of(cpu));
-		WARN_ON_ONCE(raw_smp_processor_id() != cpu);
-	}
-}
 
-static int rcu_torture_read_lock_trivial(void) __acquires(RCU)
+#endif // #else #ifdef CONFIG_TASKS_RCU
-{
-	preempt_disable();
-	return 0;
-}
 
-static void rcu_torture_read_unlock_trivial(int idx) __releases(RCU)
-{
-	preempt_enable();
-}
 
-static struct rcu_torture_ops trivial_ops = {
+#ifdef CONFIG_TASKS_RUDE_RCU
-	.ttype		= RCU_TRIVIAL_FLAVOR,
-	.init		= rcu_sync_torture_init,
-	.readlock	= rcu_torture_read_lock_trivial,
-	.read_delay	= rcu_read_delay,  /* just reuse rcu's version. */
-	.readunlock	= rcu_torture_read_unlock_trivial,
-	.readlock_held	= torture_readlock_not_held,
-	.get_gp_seq	= rcu_no_completed,
-	.sync		= synchronize_rcu_trivial,
-	.exp_sync	= synchronize_rcu_trivial,
-	.fqs		= NULL,
-	.stats		= NULL,
-	.irq_capable	= 1,
-	.name		= "trivial"
-};
 
 /*
  * Definitions for rude RCU-tasks torture testing.
@@ -851,6 +864,17 @@ static struct rcu_torture_ops tasks_rude_ops = {
 	.name		= "tasks-rude"
 };
 
+#define TASKS_RUDE_OPS &tasks_rude_ops,
+
+#else // #ifdef CONFIG_TASKS_RUDE_RCU
+
+#define TASKS_RUDE_OPS
+
+#endif // #else #ifdef CONFIG_TASKS_RUDE_RCU
+
+
+#ifdef CONFIG_TASKS_TRACE_RCU
+
 /*
  * Definitions for tracing RCU-tasks torture testing.
  */
@@ -893,6 +917,15 @@ static struct rcu_torture_ops tasks_tracing_ops = {
 	.name		= "tasks-tracing"
 };
 
+#define TASKS_TRACING_OPS &tasks_tracing_ops,
+
+#else // #ifdef CONFIG_TASKS_TRACE_RCU
+
+#define TASKS_TRACING_OPS
+
+#endif // #else #ifdef CONFIG_TASKS_TRACE_RCU
+
+
 static unsigned long rcutorture_seq_diff(unsigned long new, unsigned long old)
 {
 	if (!cur_ops->gp_diff)
@@ -1178,7 +1211,7 @@ rcu_torture_writer(void *arg)
 			 " GP expediting controlled from boot/sysfs for %s.\n",
 			 torture_type, cur_ops->name);
 	if (WARN_ONCE(nsynctypes == 0,
-		      "rcu_torture_writer: No update-side primitives.\n")) {
+		      "%s: No update-side primitives.\n", __func__)) {
 		/*
 		 * No updates primitives, so don't try updating.
 		 * The resulting test won't be testing much, hence the
@@ -1186,6 +1219,7 @@ rcu_torture_writer(void *arg)
 		 */
 		rcu_torture_writer_state = RTWS_STOPPING;
 		torture_kthread_stopping("rcu_torture_writer");
+		return 0;
 	}
 
 	do {
@@ -1322,6 +1356,17 @@ rcu_torture_fakewriter(void *arg)
 	VERBOSE_TOROUT_STRING("rcu_torture_fakewriter task started");
 	set_user_nice(current, MAX_NICE);
 
+	if (WARN_ONCE(nsynctypes == 0,
+		      "%s: No update-side primitives.\n", __func__)) {
+		/*
+		 * No updates primitives, so don't try updating.
+		 * The resulting test won't be testing much, hence the
+		 * above WARN_ONCE().
+		 */
+		torture_kthread_stopping("rcu_torture_fakewriter");
+		return 0;
+	}
+
 	do {
 		torture_hrtimeout_jiffies(torture_random(&rand) % 10, &rand);
 		if (cur_ops->cb_barrier != NULL &&
@@ -2916,10 +2961,12 @@ rcu_torture_cleanup(void)
 			pr_info("%s: Invoking %pS().\n", __func__, cur_ops->cb_barrier);
 			cur_ops->cb_barrier();
 		}
+		rcu_gp_slow_unregister(NULL);
 		return;
 	}
 	if (!cur_ops) {
 		torture_cleanup_end();
+		rcu_gp_slow_unregister(NULL);
 		return;
 	}
 
@@ -3016,6 +3063,7 @@ rcu_torture_cleanup(void)
 	else
 		rcu_torture_print_module_parms(cur_ops, "End of test: SUCCESS");
 	torture_cleanup_end();
+	rcu_gp_slow_unregister(&rcu_fwd_cb_nodelay);
 }
 
 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
@@ -3096,9 +3144,9 @@ rcu_torture_init(void)
 	int flags = 0;
 	unsigned long gp_seq = 0;
 	static struct rcu_torture_ops *torture_ops[] = {
-		&rcu_ops, &rcu_busted_ops, &srcu_ops, &srcud_ops,
+		&rcu_ops, &rcu_busted_ops, &srcu_ops, &srcud_ops, &busted_srcud_ops,
-		&busted_srcud_ops, &tasks_ops, &tasks_rude_ops,
+		TASKS_OPS TASKS_RUDE_OPS TASKS_TRACING_OPS
-		&tasks_tracing_ops, &trivial_ops,
+		&trivial_ops,
 	};
 
 	if (!torture_init_begin(torture_type, verbose))
@@ -3320,6 +3368,7 @@ rcu_torture_init(void)
 	if (object_debug)
 		rcu_test_debug_objects();
 	torture_init_end();
+	rcu_gp_slow_register(&rcu_fwd_cb_nodelay);
 	return 0;
 
 unwind:

kernel/rcu/refscale.c

@@ -207,6 +207,8 @@ static struct ref_scale_ops srcu_ops = {
 	.name		= "srcu"
 };
 
+#ifdef CONFIG_TASKS_RCU
+
 // Definitions for RCU Tasks ref scale testing: Empty read markers.
 // These definitions also work for RCU Rude readers.
 static void rcu_tasks_ref_scale_read_section(const int nloops)
@@ -232,6 +234,16 @@ static struct ref_scale_ops rcu_tasks_ops = {
 	.name		= "rcu-tasks"
 };
 
+#define RCU_TASKS_OPS &rcu_tasks_ops,
+
+#else // #ifdef CONFIG_TASKS_RCU
+
+#define RCU_TASKS_OPS
+
+#endif // #else // #ifdef CONFIG_TASKS_RCU
+
+#ifdef CONFIG_TASKS_TRACE_RCU
+
 // Definitions for RCU Tasks Trace ref scale testing.
 static void rcu_trace_ref_scale_read_section(const int nloops)
 {
@@ -261,6 +273,14 @@ static struct ref_scale_ops rcu_trace_ops = {
 	.name		= "rcu-trace"
 };
 
+#define RCU_TRACE_OPS &rcu_trace_ops,
+
+#else // #ifdef CONFIG_TASKS_TRACE_RCU
+
+#define RCU_TRACE_OPS
+
+#endif // #else // #ifdef CONFIG_TASKS_TRACE_RCU
+
 // Definitions for reference count
 static atomic_t refcnt;
 
@@ -790,7 +810,7 @@ ref_scale_init(void)
 	long i;
 	int firsterr = 0;
 	static struct ref_scale_ops *scale_ops[] = {
-		&rcu_ops, &srcu_ops, &rcu_trace_ops, &rcu_tasks_ops, &refcnt_ops, &rwlock_ops,
+		&rcu_ops, &srcu_ops, RCU_TRACE_OPS RCU_TASKS_OPS &refcnt_ops, &rwlock_ops,
 		&rwsem_ops, &lock_ops, &lock_irq_ops, &acqrel_ops, &clock_ops,
 	};
 

kernel/rcu/srcutree.c

@@ -24,6 +24,7 @@
 #include <linux/smp.h>
 #include <linux/delay.h>
 #include <linux/module.h>
+#include <linux/slab.h>
 #include <linux/srcu.h>
 
 #include "rcu.h"
@@ -38,6 +39,35 @@ module_param(exp_holdoff, ulong, 0444);
 static ulong counter_wrap_check = (ULONG_MAX >> 2);
 module_param(counter_wrap_check, ulong, 0444);
 
+/*
+ * Control conversion to SRCU_SIZE_BIG:
+ *    0: Don't convert at all.
+ *    1: Convert at init_srcu_struct() time.
+ *    2: Convert when rcutorture invokes srcu_torture_stats_print().
+ *    3: Decide at boot time based on system shape (default).
+ * 0x1x: Convert when excessive contention encountered.
+ */
+#define SRCU_SIZING_NONE	0
+#define SRCU_SIZING_INIT	1
+#define SRCU_SIZING_TORTURE	2
+#define SRCU_SIZING_AUTO	3
+#define SRCU_SIZING_CONTEND	0x10
+#define SRCU_SIZING_IS(x) ((convert_to_big & ~SRCU_SIZING_CONTEND) == x)
+#define SRCU_SIZING_IS_NONE() (SRCU_SIZING_IS(SRCU_SIZING_NONE))
+#define SRCU_SIZING_IS_INIT() (SRCU_SIZING_IS(SRCU_SIZING_INIT))
+#define SRCU_SIZING_IS_TORTURE() (SRCU_SIZING_IS(SRCU_SIZING_TORTURE))
+#define SRCU_SIZING_IS_CONTEND() (convert_to_big & SRCU_SIZING_CONTEND)
+static int convert_to_big = SRCU_SIZING_AUTO;
+module_param(convert_to_big, int, 0444);
+
+/* Number of CPUs to trigger init_srcu_struct()-time transition to big. */
+static int big_cpu_lim __read_mostly = 128;
+module_param(big_cpu_lim, int, 0444);
+
+/* Contention events per jiffy to initiate transition to big. */
+static int small_contention_lim __read_mostly = 100;
+module_param(small_contention_lim, int, 0444);
+
 /* Early-boot callback-management, so early that no lock is required! */
 static LIST_HEAD(srcu_boot_list);
 static bool __read_mostly srcu_init_done;
@@ -71,16 +101,67 @@ do {									\
 	smp_mb__after_unlock_lock();						\
 } while (0)
 
+#define spin_trylock_irqsave_rcu_node(p, flags)					\
+({										\
+	bool ___locked = spin_trylock_irqsave(&ACCESS_PRIVATE(p, lock), flags);	\
+										\
+	if (___locked)								\
+		smp_mb__after_unlock_lock();					\
+	___locked;								\
+})
+
 #define spin_unlock_irqrestore_rcu_node(p, flags)				\
 	spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags)			\
 
 /*
- * Initialize SRCU combining tree.  Note that statically allocated
+ * Initialize SRCU per-CPU data.  Note that statically allocated
  * srcu_struct structures might already have srcu_read_lock() and
  * srcu_read_unlock() running against them.  So if the is_static parameter
  * is set, don't initialize ->srcu_lock_count[] and ->srcu_unlock_count[].
  */
-static void init_srcu_struct_nodes(struct srcu_struct *ssp)
+static void init_srcu_struct_data(struct srcu_struct *ssp)
+{
+	int cpu;
+	struct srcu_data *sdp;
+
+	/*
+	 * Initialize the per-CPU srcu_data array, which feeds into the
+	 * leaves of the srcu_node tree.
+	 */
+	WARN_ON_ONCE(ARRAY_SIZE(sdp->srcu_lock_count) !=
+		     ARRAY_SIZE(sdp->srcu_unlock_count));
+	for_each_possible_cpu(cpu) {
+		sdp = per_cpu_ptr(ssp->sda, cpu);
+		spin_lock_init(&ACCESS_PRIVATE(sdp, lock));
+		rcu_segcblist_init(&sdp->srcu_cblist);
+		sdp->srcu_cblist_invoking = false;
+		sdp->srcu_gp_seq_needed = ssp->srcu_gp_seq;
+		sdp->srcu_gp_seq_needed_exp = ssp->srcu_gp_seq;
+		sdp->mynode = NULL;
+		sdp->cpu = cpu;
+		INIT_WORK(&sdp->work, srcu_invoke_callbacks);
+		timer_setup(&sdp->delay_work, srcu_delay_timer, 0);
+		sdp->ssp = ssp;
+	}
+}
+
+/* Invalid seq state, used during snp node initialization */
+#define SRCU_SNP_INIT_SEQ		0x2
+
+/*
+ * Check whether sequence number corresponding to snp node,
+ * is invalid.
+ */
+static inline bool srcu_invl_snp_seq(unsigned long s)
+{
+	return rcu_seq_state(s) == SRCU_SNP_INIT_SEQ;
+}
+
+/*
+ * Allocated and initialize SRCU combining tree.  Returns @true if
+ * allocation succeeded and @false otherwise.
+ */
+static bool init_srcu_struct_nodes(struct srcu_struct *ssp, gfp_t gfp_flags)
 {
 	int cpu;
 	int i;
@@ -92,6 +173,9 @@ static void init_srcu_struct_nodes(struct srcu_struct *ssp)
 
 	/* Initialize geometry if it has not already been initialized. */
 	rcu_init_geometry();
+	ssp->node = kcalloc(rcu_num_nodes, sizeof(*ssp->node), gfp_flags);
+	if (!ssp->node)
+		return false;
 
 	/* Work out the overall tree geometry. */
 	ssp->level[0] = &ssp->node[0];
@@ -105,10 +189,10 @@ static void init_srcu_struct_nodes(struct srcu_struct *ssp)
 		WARN_ON_ONCE(ARRAY_SIZE(snp->srcu_have_cbs) !=
 			     ARRAY_SIZE(snp->srcu_data_have_cbs));
 		for (i = 0; i < ARRAY_SIZE(snp->srcu_have_cbs); i++) {
-			snp->srcu_have_cbs[i] = 0;
+			snp->srcu_have_cbs[i] = SRCU_SNP_INIT_SEQ;
 			snp->srcu_data_have_cbs[i] = 0;
 		}
-		snp->srcu_gp_seq_needed_exp = 0;
+		snp->srcu_gp_seq_needed_exp = SRCU_SNP_INIT_SEQ;
 		snp->grplo = -1;
 		snp->grphi = -1;
 		if (snp == &ssp->node[0]) {
@@ -129,39 +213,31 @@ static void init_srcu_struct_nodes(struct srcu_struct *ssp)
 	 * Initialize the per-CPU srcu_data array, which feeds into the
 	 * leaves of the srcu_node tree.
 	 */
-	WARN_ON_ONCE(ARRAY_SIZE(sdp->srcu_lock_count) !=
-		     ARRAY_SIZE(sdp->srcu_unlock_count));
 	level = rcu_num_lvls - 1;
 	snp_first = ssp->level[level];
 	for_each_possible_cpu(cpu) {
 		sdp = per_cpu_ptr(ssp->sda, cpu);
-		spin_lock_init(&ACCESS_PRIVATE(sdp, lock));
-		rcu_segcblist_init(&sdp->srcu_cblist);
-		sdp->srcu_cblist_invoking = false;
-		sdp->srcu_gp_seq_needed = ssp->srcu_gp_seq;
-		sdp->srcu_gp_seq_needed_exp = ssp->srcu_gp_seq;
 		sdp->mynode = &snp_first[cpu / levelspread[level]];
 		for (snp = sdp->mynode; snp != NULL; snp = snp->srcu_parent) {
 			if (snp->grplo < 0)
 				snp->grplo = cpu;
 			snp->grphi = cpu;
 		}
-		sdp->cpu = cpu;
-		INIT_WORK(&sdp->work, srcu_invoke_callbacks);
-		timer_setup(&sdp->delay_work, srcu_delay_timer, 0);
-		sdp->ssp = ssp;
 		sdp->grpmask = 1 << (cpu - sdp->mynode->grplo);
 	}
+	smp_store_release(&ssp->srcu_size_state, SRCU_SIZE_WAIT_BARRIER);
+	return true;
 }
 
 /*
  * Initialize non-compile-time initialized fields, including the
- * associated srcu_node and srcu_data structures.  The is_static
+ * associated srcu_node and srcu_data structures.  The is_static parameter
- * parameter is passed through to init_srcu_struct_nodes(), and
+ * tells us that ->sda has already been wired up to srcu_data.
- * also tells us that ->sda has already been wired up to srcu_data.
  */
 static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
 {
+	ssp->srcu_size_state = SRCU_SIZE_SMALL;
+	ssp->node = NULL;
 	mutex_init(&ssp->srcu_cb_mutex);
 	mutex_init(&ssp->srcu_gp_mutex);
 	ssp->srcu_idx = 0;
@@ -170,13 +246,25 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
 	mutex_init(&ssp->srcu_barrier_mutex);
 	atomic_set(&ssp->srcu_barrier_cpu_cnt, 0);
 	INIT_DELAYED_WORK(&ssp->work, process_srcu);
+	ssp->sda_is_static = is_static;
 	if (!is_static)
 		ssp->sda = alloc_percpu(struct srcu_data);
 	if (!ssp->sda)
 		return -ENOMEM;
-	init_srcu_struct_nodes(ssp);
+	init_srcu_struct_data(ssp);
 	ssp->srcu_gp_seq_needed_exp = 0;
 	ssp->srcu_last_gp_end = ktime_get_mono_fast_ns();
+	if (READ_ONCE(ssp->srcu_size_state) == SRCU_SIZE_SMALL && SRCU_SIZING_IS_INIT()) {
+		if (!init_srcu_struct_nodes(ssp, GFP_ATOMIC)) {
+			if (!ssp->sda_is_static) {
+				free_percpu(ssp->sda);
+				ssp->sda = NULL;
+				return -ENOMEM;
+			}
+		} else {
+			WRITE_ONCE(ssp->srcu_size_state, SRCU_SIZE_BIG);
+		}
+	}
 	smp_store_release(&ssp->srcu_gp_seq_needed, 0); /* Init done. */
 	return 0;
 }
@@ -213,6 +301,86 @@ EXPORT_SYMBOL_GPL(init_srcu_struct);
 
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
+/*
+ * Initiate a transition to SRCU_SIZE_BIG with lock held.
+ */
+static void __srcu_transition_to_big(struct srcu_struct *ssp)
+{
+	lockdep_assert_held(&ACCESS_PRIVATE(ssp, lock));
+	smp_store_release(&ssp->srcu_size_state, SRCU_SIZE_ALLOC);
+}
+
+/*
+ * Initiate an idempotent transition to SRCU_SIZE_BIG.
+ */
+static void srcu_transition_to_big(struct srcu_struct *ssp)
+{
+	unsigned long flags;
+
+	/* Double-checked locking on ->srcu_size-state. */
+	if (smp_load_acquire(&ssp->srcu_size_state) != SRCU_SIZE_SMALL)
+		return;
+	spin_lock_irqsave_rcu_node(ssp, flags);
+	if (smp_load_acquire(&ssp->srcu_size_state) != SRCU_SIZE_SMALL) {
+		spin_unlock_irqrestore_rcu_node(ssp, flags);
+		return;
+	}
+	__srcu_transition_to_big(ssp);
+	spin_unlock_irqrestore_rcu_node(ssp, flags);
+}
+
+/*
+ * Check to see if the just-encountered contention event justifies
+ * a transition to SRCU_SIZE_BIG.
+ */
+static void spin_lock_irqsave_check_contention(struct srcu_struct *ssp)
+{
+	unsigned long j;
+
+	if (!SRCU_SIZING_IS_CONTEND() || ssp->srcu_size_state)
+		return;
+	j = jiffies;
+	if (ssp->srcu_size_jiffies != j) {
+		ssp->srcu_size_jiffies = j;
+		ssp->srcu_n_lock_retries = 0;
+	}
+	if (++ssp->srcu_n_lock_retries <= small_contention_lim)
+		return;
+	__srcu_transition_to_big(ssp);
+}
+
+/*
+ * Acquire the specified srcu_data structure's ->lock, but check for
+ * excessive contention, which results in initiation of a transition
+ * to SRCU_SIZE_BIG.  But only if the srcutree.convert_to_big module
+ * parameter permits this.
+ */
+static void spin_lock_irqsave_sdp_contention(struct srcu_data *sdp, unsigned long *flags)
+{
+	struct srcu_struct *ssp = sdp->ssp;
+
+	if (spin_trylock_irqsave_rcu_node(sdp, *flags))
+		return;
+	spin_lock_irqsave_rcu_node(ssp, *flags);
+	spin_lock_irqsave_check_contention(ssp);
+	spin_unlock_irqrestore_rcu_node(ssp, *flags);
+	spin_lock_irqsave_rcu_node(sdp, *flags);
+}
+
+/*
+ * Acquire the specified srcu_struct structure's ->lock, but check for
+ * excessive contention, which results in initiation of a transition
+ * to SRCU_SIZE_BIG.  But only if the srcutree.convert_to_big module
+ * parameter permits this.
+ */
+static void spin_lock_irqsave_ssp_contention(struct srcu_struct *ssp, unsigned long *flags)
+{
+	if (spin_trylock_irqsave_rcu_node(ssp, *flags))
+		return;
+	spin_lock_irqsave_rcu_node(ssp, *flags);
+	spin_lock_irqsave_check_contention(ssp);
+}
+
 /*
  * First-use initialization of statically allocated srcu_struct
  * structure.  Wiring up the combining tree is more than can be
@@ -343,7 +511,10 @@ static bool srcu_readers_active(struct srcu_struct *ssp)
 	return sum;
 }
 
-#define SRCU_INTERVAL		1
+#define SRCU_INTERVAL		1	// Base delay if no expedited GPs pending.
+#define SRCU_MAX_INTERVAL	10	// Maximum incremental delay from slow readers.
+#define SRCU_MAX_NODELAY_PHASE	1	// Maximum per-GP-phase consecutive no-delay instances.
+#define SRCU_MAX_NODELAY	100	// Maximum consecutive no-delay instances.
 
 /*
  * Return grace-period delay, zero if there are expedited grace
@@ -351,10 +522,18 @@ static bool srcu_readers_active(struct srcu_struct *ssp)
  */
 static unsigned long srcu_get_delay(struct srcu_struct *ssp)
 {
-	if (ULONG_CMP_LT(READ_ONCE(ssp->srcu_gp_seq),
+	unsigned long jbase = SRCU_INTERVAL;
-			 READ_ONCE(ssp->srcu_gp_seq_needed_exp)))
+
-		return 0;
+	if (ULONG_CMP_LT(READ_ONCE(ssp->srcu_gp_seq), READ_ONCE(ssp->srcu_gp_seq_needed_exp)))
-	return SRCU_INTERVAL;
+		jbase = 0;
+	if (rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)))
+		jbase += jiffies - READ_ONCE(ssp->srcu_gp_start);
+	if (!jbase) {
+		WRITE_ONCE(ssp->srcu_n_exp_nodelay, READ_ONCE(ssp->srcu_n_exp_nodelay) + 1);
+		if (READ_ONCE(ssp->srcu_n_exp_nodelay) > SRCU_MAX_NODELAY_PHASE)
+			jbase = 1;
+	}
+	return jbase > SRCU_MAX_INTERVAL ? SRCU_MAX_INTERVAL : jbase;
 }
 
 /**
@@ -382,14 +561,21 @@ void cleanup_srcu_struct(struct srcu_struct *ssp)
 			return; /* Forgot srcu_barrier(), so just leak it! */
 	}
 	if (WARN_ON(rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) != SRCU_STATE_IDLE) ||
+	    WARN_ON(rcu_seq_current(&ssp->srcu_gp_seq) != ssp->srcu_gp_seq_needed) ||
 	    WARN_ON(srcu_readers_active(ssp))) {
-		pr_info("%s: Active srcu_struct %p state: %d\n",
+		pr_info("%s: Active srcu_struct %p read state: %d gp state: %lu/%lu\n",
-			__func__, ssp, rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)));
+			__func__, ssp, rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)),
+			rcu_seq_current(&ssp->srcu_gp_seq), ssp->srcu_gp_seq_needed);
 		return; /* Caller forgot to stop doing call_srcu()? */
 	}
+	if (!ssp->sda_is_static) {
 		free_percpu(ssp->sda);
 		ssp->sda = NULL;
 	}
+	kfree(ssp->node);
+	ssp->node = NULL;
+	ssp->srcu_size_state = SRCU_SIZE_SMALL;
+}
 EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
 
 /*
@@ -434,9 +620,13 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
  */
 static void srcu_gp_start(struct srcu_struct *ssp)
 {
-	struct srcu_data *sdp = this_cpu_ptr(ssp->sda);
+	struct srcu_data *sdp;
 	int state;
 
+	if (smp_load_acquire(&ssp->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER)
+		sdp = per_cpu_ptr(ssp->sda, 0);
+	else
+		sdp = this_cpu_ptr(ssp->sda);
 	lockdep_assert_held(&ACCESS_PRIVATE(ssp, lock));
 	WARN_ON_ONCE(ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed));
 	spin_lock_rcu_node(sdp);  /* Interrupts already disabled. */
@@ -445,6 +635,8 @@ static void srcu_gp_start(struct srcu_struct *ssp)
 	(void)rcu_segcblist_accelerate(&sdp->srcu_cblist,
 				       rcu_seq_snap(&ssp->srcu_gp_seq));
 	spin_unlock_rcu_node(sdp);  /* Interrupts remain disabled. */
+	WRITE_ONCE(ssp->srcu_gp_start, jiffies);
+	WRITE_ONCE(ssp->srcu_n_exp_nodelay, 0);
 	smp_mb(); /* Order prior store to ->srcu_gp_seq_needed vs. GP start. */
 	rcu_seq_start(&ssp->srcu_gp_seq);
 	state = rcu_seq_state(ssp->srcu_gp_seq);
@@ -517,7 +709,9 @@ static void srcu_gp_end(struct srcu_struct *ssp)
 	int idx;
 	unsigned long mask;
 	struct srcu_data *sdp;
+	unsigned long sgsne;
 	struct srcu_node *snp;
+	int ss_state;
 
 	/* Prevent more than one additional grace period. */
 	mutex_lock(&ssp->srcu_cb_mutex);
@@ -526,7 +720,7 @@ static void srcu_gp_end(struct srcu_struct *ssp)
 	spin_lock_irq_rcu_node(ssp);
 	idx = rcu_seq_state(ssp->srcu_gp_seq);
 	WARN_ON_ONCE(idx != SRCU_STATE_SCAN2);
-	cbdelay = srcu_get_delay(ssp);
+	cbdelay = !!srcu_get_delay(ssp);
 	WRITE_ONCE(ssp->srcu_last_gp_end, ktime_get_mono_fast_ns());
 	rcu_seq_end(&ssp->srcu_gp_seq);
 	gpseq = rcu_seq_current(&ssp->srcu_gp_seq);
@@ -537,37 +731,44 @@ static void srcu_gp_end(struct srcu_struct *ssp)
 	/* A new grace period can start at this point.  But only one. */
 
 	/* Initiate callback invocation as needed. */
+	ss_state = smp_load_acquire(&ssp->srcu_size_state);
+	if (ss_state < SRCU_SIZE_WAIT_BARRIER) {
+		srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, 0), cbdelay);
+	} else {
 		idx = rcu_seq_ctr(gpseq) % ARRAY_SIZE(snp->srcu_have_cbs);
 		srcu_for_each_node_breadth_first(ssp, snp) {
 			spin_lock_irq_rcu_node(snp);
 			cbs = false;
 			last_lvl = snp >= ssp->level[rcu_num_lvls - 1];
 			if (last_lvl)
-			cbs = snp->srcu_have_cbs[idx] == gpseq;
+				cbs = ss_state < SRCU_SIZE_BIG || snp->srcu_have_cbs[idx] == gpseq;
 			snp->srcu_have_cbs[idx] = gpseq;
 			rcu_seq_set_state(&snp->srcu_have_cbs[idx], 1);
-		if (ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, gpseq))
+			sgsne = snp->srcu_gp_seq_needed_exp;
+			if (srcu_invl_snp_seq(sgsne) || ULONG_CMP_LT(sgsne, gpseq))
 				WRITE_ONCE(snp->srcu_gp_seq_needed_exp, gpseq);
+			if (ss_state < SRCU_SIZE_BIG)
+				mask = ~0;
+			else
 				mask = snp->srcu_data_have_cbs[idx];
 			snp->srcu_data_have_cbs[idx] = 0;
 			spin_unlock_irq_rcu_node(snp);
 			if (cbs)
 				srcu_schedule_cbs_snp(ssp, snp, mask, cbdelay);
+		}
+	}
 
 	/* Occasionally prevent srcu_data counter wrap. */
-		if (!(gpseq & counter_wrap_check) && last_lvl)
+	if (!(gpseq & counter_wrap_check))
-			for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) {
+		for_each_possible_cpu(cpu) {
 			sdp = per_cpu_ptr(ssp->sda, cpu);
 			spin_lock_irqsave_rcu_node(sdp, flags);
-				if (ULONG_CMP_GE(gpseq,
+			if (ULONG_CMP_GE(gpseq, sdp->srcu_gp_seq_needed + 100))
-						 sdp->srcu_gp_seq_needed + 100))
 				sdp->srcu_gp_seq_needed = gpseq;
-				if (ULONG_CMP_GE(gpseq,
+			if (ULONG_CMP_GE(gpseq, sdp->srcu_gp_seq_needed_exp + 100))
-						 sdp->srcu_gp_seq_needed_exp + 100))
 				sdp->srcu_gp_seq_needed_exp = gpseq;
 			spin_unlock_irqrestore_rcu_node(sdp, flags);
 		}
-	}
 
 	/* Callback initiation done, allow grace periods after next. */
 	mutex_unlock(&ssp->srcu_cb_mutex);
@@ -583,6 +784,14 @@ static void srcu_gp_end(struct srcu_struct *ssp)
 	} else {
 		spin_unlock_irq_rcu_node(ssp);
 	}
+
+	/* Transition to big if needed. */
+	if (ss_state != SRCU_SIZE_SMALL && ss_state != SRCU_SIZE_BIG) {
+		if (ss_state == SRCU_SIZE_ALLOC)
+			init_srcu_struct_nodes(ssp, GFP_KERNEL);
+		else
+			smp_store_release(&ssp->srcu_size_state, ss_state + 1);
+	}
 }
 
 /*
@@ -596,20 +805,24 @@ static void srcu_funnel_exp_start(struct srcu_struct *ssp, struct srcu_node *snp
 				  unsigned long s)
 {
 	unsigned long flags;
+	unsigned long sgsne;
 
+	if (snp)
 		for (; snp != NULL; snp = snp->srcu_parent) {
+			sgsne = READ_ONCE(snp->srcu_gp_seq_needed_exp);
 			if (rcu_seq_done(&ssp->srcu_gp_seq, s) ||
-		    ULONG_CMP_GE(READ_ONCE(snp->srcu_gp_seq_needed_exp), s))
+			    (!srcu_invl_snp_seq(sgsne) && ULONG_CMP_GE(sgsne, s)))
 				return;
 			spin_lock_irqsave_rcu_node(snp, flags);
-		if (ULONG_CMP_GE(snp->srcu_gp_seq_needed_exp, s)) {
+			sgsne = snp->srcu_gp_seq_needed_exp;
+			if (!srcu_invl_snp_seq(sgsne) && ULONG_CMP_GE(sgsne, s)) {
 				spin_unlock_irqrestore_rcu_node(snp, flags);
 				return;
 			}
 			WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s);
 			spin_unlock_irqrestore_rcu_node(snp, flags);
 		}
-	spin_lock_irqsave_rcu_node(ssp, flags);
+	spin_lock_irqsave_ssp_contention(ssp, &flags);
 	if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, s))
 		WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, s);
 	spin_unlock_irqrestore_rcu_node(ssp, flags);
@@ -630,23 +843,30 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp,
 {
 	unsigned long flags;
 	int idx = rcu_seq_ctr(s) % ARRAY_SIZE(sdp->mynode->srcu_have_cbs);
-	struct srcu_node *snp = sdp->mynode;
+	unsigned long sgsne;
+	struct srcu_node *snp;
+	struct srcu_node *snp_leaf;
 	unsigned long snp_seq;
 
+	/* Ensure that snp node tree is fully initialized before traversing it */
+	if (smp_load_acquire(&ssp->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER)
+		snp_leaf = NULL;
+	else
+		snp_leaf = sdp->mynode;
+
+	if (snp_leaf)
 		/* Each pass through the loop does one level of the srcu_node tree. */
-	for (; snp != NULL; snp = snp->srcu_parent) {
+		for (snp = snp_leaf; snp != NULL; snp = snp->srcu_parent) {
-		if (rcu_seq_done(&ssp->srcu_gp_seq, s) && snp != sdp->mynode)
+			if (rcu_seq_done(&ssp->srcu_gp_seq, s) && snp != snp_leaf)
 				return; /* GP already done and CBs recorded. */
 			spin_lock_irqsave_rcu_node(snp, flags);
-		if (ULONG_CMP_GE(snp->srcu_have_cbs[idx], s)) {
 			snp_seq = snp->srcu_have_cbs[idx];
-			if (snp == sdp->mynode && snp_seq == s)
+			if (!srcu_invl_snp_seq(snp_seq) && ULONG_CMP_GE(snp_seq, s)) {
+				if (snp == snp_leaf && snp_seq == s)
 					snp->srcu_data_have_cbs[idx] |= sdp->grpmask;
 				spin_unlock_irqrestore_rcu_node(snp, flags);
-			if (snp == sdp->mynode && snp_seq != s) {
+				if (snp == snp_leaf && snp_seq != s) {
-				srcu_schedule_cbs_sdp(sdp, do_norm
+					srcu_schedule_cbs_sdp(sdp, do_norm ? SRCU_INTERVAL : 0);
-							   ? SRCU_INTERVAL
-							   : 0);
 					return;
 				}
 				if (!do_norm)
@@ -654,15 +874,16 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp,
 				return;
 			}
 			snp->srcu_have_cbs[idx] = s;
-		if (snp == sdp->mynode)
+			if (snp == snp_leaf)
 				snp->srcu_data_have_cbs[idx] |= sdp->grpmask;
-		if (!do_norm && ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, s))
+			sgsne = snp->srcu_gp_seq_needed_exp;
+			if (!do_norm && (srcu_invl_snp_seq(sgsne) || ULONG_CMP_LT(sgsne, s)))
 				WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s);
 			spin_unlock_irqrestore_rcu_node(snp, flags);
 		}
 
 	/* Top of tree, must ensure the grace period will be started. */
-	spin_lock_irqsave_rcu_node(ssp, flags);
+	spin_lock_irqsave_ssp_contention(ssp, &flags);
 	if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed, s)) {
 		/*
 		 * Record need for grace period s.  Pair with load
@@ -678,9 +899,15 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp,
 	    rcu_seq_state(ssp->srcu_gp_seq) == SRCU_STATE_IDLE) {
 		WARN_ON_ONCE(ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed));
 		srcu_gp_start(ssp);
+
+		// And how can that list_add() in the "else" clause
+		// possibly be safe for concurrent execution?  Well,
+		// it isn't.  And it does not have to be.  After all, it
+		// can only be executed during early boot when there is only
+		// the one boot CPU running with interrupts still disabled.
 		if (likely(srcu_init_done))
 			queue_delayed_work(rcu_gp_wq, &ssp->work,
-					   srcu_get_delay(ssp));
+					   !!srcu_get_delay(ssp));
 		else if (list_empty(&ssp->work.work.entry))
 			list_add(&ssp->work.work.entry, &srcu_boot_list);
 	}
@@ -814,11 +1041,17 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
 	bool needgp = false;
 	unsigned long s;
 	struct srcu_data *sdp;
+	struct srcu_node *sdp_mynode;
+	int ss_state;
 
 	check_init_srcu_struct(ssp);
 	idx = srcu_read_lock(ssp);
+	ss_state = smp_load_acquire(&ssp->srcu_size_state);
+	if (ss_state < SRCU_SIZE_WAIT_CALL)
+		sdp = per_cpu_ptr(ssp->sda, 0);
+	else
 		sdp = raw_cpu_ptr(ssp->sda);
-	spin_lock_irqsave_rcu_node(sdp, flags);
+	spin_lock_irqsave_sdp_contention(sdp, &flags);
 	if (rhp)
 		rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
 	rcu_segcblist_advance(&sdp->srcu_cblist,
@@ -834,10 +1067,17 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
 		needexp = true;
 	}
 	spin_unlock_irqrestore_rcu_node(sdp, flags);
+
+	/* Ensure that snp node tree is fully initialized before traversing it */
+	if (ss_state < SRCU_SIZE_WAIT_BARRIER)
+		sdp_mynode = NULL;
+	else
+		sdp_mynode = sdp->mynode;
+
 	if (needgp)
 		srcu_funnel_gp_start(ssp, sdp, s, do_norm);
 	else if (needexp)
-		srcu_funnel_exp_start(ssp, sdp->mynode, s);
+		srcu_funnel_exp_start(ssp, sdp_mynode, s);
 	srcu_read_unlock(ssp, idx);
 	return s;
 }
@@ -1097,6 +1337,28 @@ static void srcu_barrier_cb(struct rcu_head *rhp)
 		complete(&ssp->srcu_barrier_completion);
 }
 
+/*
+ * Enqueue an srcu_barrier() callback on the specified srcu_data
+ * structure's ->cblist.  but only if that ->cblist already has at least one
+ * callback enqueued.  Note that if a CPU already has callbacks enqueue,
+ * it must have already registered the need for a future grace period,
+ * so all we need do is enqueue a callback that will use the same grace
+ * period as the last callback already in the queue.
+ */
+static void srcu_barrier_one_cpu(struct srcu_struct *ssp, struct srcu_data *sdp)
+{
+	spin_lock_irq_rcu_node(sdp);
+	atomic_inc(&ssp->srcu_barrier_cpu_cnt);
+	sdp->srcu_barrier_head.func = srcu_barrier_cb;
+	debug_rcu_head_queue(&sdp->srcu_barrier_head);
+	if (!rcu_segcblist_entrain(&sdp->srcu_cblist,
+				   &sdp->srcu_barrier_head)) {
+		debug_rcu_head_unqueue(&sdp->srcu_barrier_head);
+		atomic_dec(&ssp->srcu_barrier_cpu_cnt);
+	}
+	spin_unlock_irq_rcu_node(sdp);
+}
+
 /**
  * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
  * @ssp: srcu_struct on which to wait for in-flight callbacks.
@@ -1104,7 +1366,7 @@ static void srcu_barrier_cb(struct rcu_head *rhp)
 void srcu_barrier(struct srcu_struct *ssp)
 {
 	int cpu;
-	struct srcu_data *sdp;
+	int idx;
 	unsigned long s = rcu_seq_snap(&ssp->srcu_barrier_seq);
 
 	check_init_srcu_struct(ssp);
@@ -1120,27 +1382,13 @@ void srcu_barrier(struct srcu_struct *ssp)
 	/* Initial count prevents reaching zero until all CBs are posted. */
 	atomic_set(&ssp->srcu_barrier_cpu_cnt, 1);
 
-	/*
+	idx = srcu_read_lock(ssp);
-	 * Each pass through this loop enqueues a callback, but only
+	if (smp_load_acquire(&ssp->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER)
-	 * on CPUs already having callbacks enqueued.  Note that if
+		srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, 0));
-	 * a CPU already has callbacks enqueue, it must have already
+	else
-	 * registered the need for a future grace period, so all we
+		for_each_possible_cpu(cpu)
-	 * need do is enqueue a callback that will use the same
+			srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, cpu));
-	 * grace period as the last callback already in the queue.
+	srcu_read_unlock(ssp, idx);
-	 */
-	for_each_possible_cpu(cpu) {
-		sdp = per_cpu_ptr(ssp->sda, cpu);
-		spin_lock_irq_rcu_node(sdp);
-		atomic_inc(&ssp->srcu_barrier_cpu_cnt);
-		sdp->srcu_barrier_head.func = srcu_barrier_cb;
-		debug_rcu_head_queue(&sdp->srcu_barrier_head);
-		if (!rcu_segcblist_entrain(&sdp->srcu_cblist,
-					   &sdp->srcu_barrier_head)) {
-			debug_rcu_head_unqueue(&sdp->srcu_barrier_head);
-			atomic_dec(&ssp->srcu_barrier_cpu_cnt);
-		}
-		spin_unlock_irq_rcu_node(sdp);
-	}
 
 	/* Remove the initial count, at which point reaching zero can happen. */
 	if (atomic_dec_and_test(&ssp->srcu_barrier_cpu_cnt))
@@ -1214,6 +1462,7 @@ static void srcu_advance_state(struct srcu_struct *ssp)
 		srcu_flip(ssp);
 		spin_lock_irq_rcu_node(ssp);
 		rcu_seq_set_state(&ssp->srcu_gp_seq, SRCU_STATE_SCAN2);
+		ssp->srcu_n_exp_nodelay = 0;
 		spin_unlock_irq_rcu_node(ssp);
 	}
 
@@ -1228,6 +1477,7 @@ static void srcu_advance_state(struct srcu_struct *ssp)
 			mutex_unlock(&ssp->srcu_gp_mutex);
 			return; /* readers present, retry later. */
 		}
+		ssp->srcu_n_exp_nodelay = 0;
 		srcu_gp_end(ssp);  /* Releases ->srcu_gp_mutex. */
 	}
 }
@@ -1318,12 +1568,28 @@ static void srcu_reschedule(struct srcu_struct *ssp, unsigned long delay)
  */
 static void process_srcu(struct work_struct *work)
 {
+	unsigned long curdelay;
+	unsigned long j;
 	struct srcu_struct *ssp;
 
 	ssp = container_of(work, struct srcu_struct, work.work);
 
 	srcu_advance_state(ssp);
-	srcu_reschedule(ssp, srcu_get_delay(ssp));
+	curdelay = srcu_get_delay(ssp);
+	if (curdelay) {
+		WRITE_ONCE(ssp->reschedule_count, 0);
+	} else {
+		j = jiffies;
+		if (READ_ONCE(ssp->reschedule_jiffies) == j) {
+			WRITE_ONCE(ssp->reschedule_count, READ_ONCE(ssp->reschedule_count) + 1);
+			if (READ_ONCE(ssp->reschedule_count) > SRCU_MAX_NODELAY)
+				curdelay = 1;
+		} else {
+			WRITE_ONCE(ssp->reschedule_count, 1);
+			WRITE_ONCE(ssp->reschedule_jiffies, j);
+		}
+	}
+	srcu_reschedule(ssp, curdelay);
 }
 
 void srcutorture_get_gp_data(enum rcutorture_type test_type,
@@ -1337,15 +1603,38 @@ void srcutorture_get_gp_data(enum rcutorture_type test_type,
 }
 EXPORT_SYMBOL_GPL(srcutorture_get_gp_data);
 
+static const char * const srcu_size_state_name[] = {
+	"SRCU_SIZE_SMALL",
+	"SRCU_SIZE_ALLOC",
+	"SRCU_SIZE_WAIT_BARRIER",
+	"SRCU_SIZE_WAIT_CALL",
+	"SRCU_SIZE_WAIT_CBS1",
+	"SRCU_SIZE_WAIT_CBS2",
+	"SRCU_SIZE_WAIT_CBS3",
+	"SRCU_SIZE_WAIT_CBS4",
+	"SRCU_SIZE_BIG",
+	"SRCU_SIZE_???",
+};
+
 void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf)
 {
 	int cpu;
 	int idx;
 	unsigned long s0 = 0, s1 = 0;
+	int ss_state = READ_ONCE(ssp->srcu_size_state);
+	int ss_state_idx = ss_state;
 
 	idx = ssp->srcu_idx & 0x1;
-	pr_alert("%s%s Tree SRCU g%ld per-CPU(idx=%d):",
+	if (ss_state < 0 || ss_state >= ARRAY_SIZE(srcu_size_state_name))
-		 tt, tf, rcu_seq_current(&ssp->srcu_gp_seq), idx);
+		ss_state_idx = ARRAY_SIZE(srcu_size_state_name) - 1;
+	pr_alert("%s%s Tree SRCU g%ld state %d (%s)",
+		 tt, tf, rcu_seq_current(&ssp->srcu_gp_seq), ss_state,
+		 srcu_size_state_name[ss_state_idx]);
+	if (!ssp->sda) {
+		// Called after cleanup_srcu_struct(), perhaps.
+		pr_cont(" No per-CPU srcu_data structures (->sda == NULL).\n");
+	} else {
+		pr_cont(" per-CPU(idx=%d):", idx);
 		for_each_possible_cpu(cpu) {
 			unsigned long l0, l1;
 			unsigned long u0, u1;
@@ -1375,6 +1664,9 @@ void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf)
 		}
 		pr_cont(" T(%ld,%ld)\n", s0, s1);
 	}
+	if (SRCU_SIZING_IS_TORTURE())
+		srcu_transition_to_big(ssp);
+}
 EXPORT_SYMBOL_GPL(srcu_torture_stats_print);
 
 static int __init srcu_bootup_announce(void)
@@ -1390,6 +1682,17 @@ void __init srcu_init(void)
 {
 	struct srcu_struct *ssp;
 
+	/* Decide on srcu_struct-size strategy. */
+	if (SRCU_SIZING_IS(SRCU_SIZING_AUTO)) {
+		if (nr_cpu_ids >= big_cpu_lim) {
+			convert_to_big = SRCU_SIZING_INIT; // Don't bother waiting for contention.
+			pr_info("%s: Setting srcu_struct sizes to big.\n", __func__);
+		} else {
+			convert_to_big = SRCU_SIZING_NONE | SRCU_SIZING_CONTEND;
+			pr_info("%s: Setting srcu_struct sizes based on contention.\n", __func__);
+		}
+	}
+
 	/*
 	 * Once that is set, call_srcu() can follow the normal path and
 	 * queue delayed work. This must follow RCU workqueues creation
@@ -1400,6 +1703,8 @@ void __init srcu_init(void)
 		ssp = list_first_entry(&srcu_boot_list, struct srcu_struct,
 				      work.work.entry);
 		list_del_init(&ssp->work.work.entry);
+		if (SRCU_SIZING_IS(SRCU_SIZING_INIT) && ssp->srcu_size_state == SRCU_SIZE_SMALL)
+			ssp->srcu_size_state = SRCU_SIZE_ALLOC;
 		queue_work(rcu_gp_wq, &ssp->work.work);
 	}
 }

kernel/rcu/sync.c

@@ -111,7 +111,7 @@ static void rcu_sync_func(struct rcu_head *rhp)
  * a slowpath during the update.  After this function returns, all
  * subsequent calls to rcu_sync_is_idle() will return false, which
  * tells readers to stay off their fastpaths.  A later call to
- * rcu_sync_exit() re-enables reader slowpaths.
+ * rcu_sync_exit() re-enables reader fastpaths.
  *
  * When called in isolation, rcu_sync_enter() must wait for a grace
  * period, however, closely spaced calls to rcu_sync_enter() can

kernel/rcu/tasks.h

@@ -46,7 +46,7 @@ struct rcu_tasks_percpu {
 
 /**
  * struct rcu_tasks - Definition for a Tasks-RCU-like mechanism.
- * @cbs_wq: Wait queue allowing new callback to get kthread's attention.
+ * @cbs_wait: RCU wait allowing a new callback to get kthread's attention.
  * @cbs_gbl_lock: Lock protecting callback list.
  * @kthread_ptr: This flavor's grace-period/callback-invocation kthread.
  * @gp_func: This flavor's grace-period-wait function.
@@ -77,7 +77,7 @@ struct rcu_tasks_percpu {
  * @kname: This flavor's kthread name.
  */
 struct rcu_tasks {
-	struct wait_queue_head cbs_wq;
+	struct rcuwait cbs_wait;
 	raw_spinlock_t cbs_gbl_lock;
 	int gp_state;
 	int gp_sleep;
@@ -113,11 +113,11 @@ static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp);
 #define DEFINE_RCU_TASKS(rt_name, gp, call, n)						\
 static DEFINE_PER_CPU(struct rcu_tasks_percpu, rt_name ## __percpu) = {			\
 	.lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name ## __percpu.cbs_pcpu_lock),		\
-	.rtp_irq_work = IRQ_WORK_INIT(call_rcu_tasks_iw_wakeup),			\
+	.rtp_irq_work = IRQ_WORK_INIT_HARD(call_rcu_tasks_iw_wakeup),			\
 };											\
 static struct rcu_tasks rt_name =							\
 {											\
-	.cbs_wq = __WAIT_QUEUE_HEAD_INITIALIZER(rt_name.cbs_wq),			\
+	.cbs_wait = __RCUWAIT_INITIALIZER(rt_name.wait),				\
 	.cbs_gbl_lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name.cbs_gbl_lock),			\
 	.gp_func = gp,									\
 	.call_func = call,								\
@@ -143,6 +143,11 @@ module_param(rcu_task_ipi_delay, int, 0644);
 #define RCU_TASK_STALL_TIMEOUT (HZ * 60 * 10)
 static int rcu_task_stall_timeout __read_mostly = RCU_TASK_STALL_TIMEOUT;
 module_param(rcu_task_stall_timeout, int, 0644);
+#define RCU_TASK_STALL_INFO (HZ * 10)
+static int rcu_task_stall_info __read_mostly = RCU_TASK_STALL_INFO;
+module_param(rcu_task_stall_info, int, 0644);
+static int rcu_task_stall_info_mult __read_mostly = 3;
+module_param(rcu_task_stall_info_mult, int, 0444);
 
 static int rcu_task_enqueue_lim __read_mostly = -1;
 module_param(rcu_task_enqueue_lim, int, 0444);
@@ -261,14 +266,16 @@ static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp)
 	struct rcu_tasks_percpu *rtpcp = container_of(iwp, struct rcu_tasks_percpu, rtp_irq_work);
 
 	rtp = rtpcp->rtpp;
-	wake_up(&rtp->cbs_wq);
+	rcuwait_wake_up(&rtp->cbs_wait);
 }
 
 // Enqueue a callback for the specified flavor of Tasks RCU.
 static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
 				   struct rcu_tasks *rtp)
 {
+	int chosen_cpu;
 	unsigned long flags;
+	int ideal_cpu;
 	unsigned long j;
 	bool needadjust = false;
 	bool needwake;
@@ -278,8 +285,9 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
 	rhp->func = func;
 	local_irq_save(flags);
 	rcu_read_lock();
-	rtpcp = per_cpu_ptr(rtp->rtpcpu,
+	ideal_cpu = smp_processor_id() >> READ_ONCE(rtp->percpu_enqueue_shift);
-			    smp_processor_id() >> READ_ONCE(rtp->percpu_enqueue_shift));
+	chosen_cpu = cpumask_next(ideal_cpu - 1, cpu_possible_mask);
+	rtpcp = per_cpu_ptr(rtp->rtpcpu, chosen_cpu);
 	if (!raw_spin_trylock_rcu_node(rtpcp)) { // irqs already disabled.
 		raw_spin_lock_rcu_node(rtpcp); // irqs already disabled.
 		j = jiffies;
@@ -460,7 +468,7 @@ static void rcu_tasks_invoke_cbs(struct rcu_tasks *rtp, struct rcu_tasks_percpu
 		}
 	}
 
-	if (rcu_segcblist_empty(&rtpcp->cblist))
+	if (rcu_segcblist_empty(&rtpcp->cblist) || !cpu_possible(cpu))
 		return;
 	raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
 	rcu_segcblist_advance(&rtpcp->cblist, rcu_seq_current(&rtp->tasks_gp_seq));
@@ -509,7 +517,9 @@ static int __noreturn rcu_tasks_kthread(void *arg)
 		set_tasks_gp_state(rtp, RTGS_WAIT_CBS);
 
 		/* If there were none, wait a bit and start over. */
-		wait_event_idle(rtp->cbs_wq, (needgpcb = rcu_tasks_need_gpcb(rtp)));
+		rcuwait_wait_event(&rtp->cbs_wait,
+				   (needgpcb = rcu_tasks_need_gpcb(rtp)),
+				   TASK_IDLE);
 
 		if (needgpcb & 0x2) {
 			// Wait for one grace period.
@@ -548,8 +558,15 @@ static void __init rcu_spawn_tasks_kthread_generic(struct rcu_tasks *rtp)
 static void __init rcu_tasks_bootup_oddness(void)
 {
 #if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU)
+	int rtsimc;
+
 	if (rcu_task_stall_timeout != RCU_TASK_STALL_TIMEOUT)
 		pr_info("\tTasks-RCU CPU stall warnings timeout set to %d (rcu_task_stall_timeout).\n", rcu_task_stall_timeout);
+	rtsimc = clamp(rcu_task_stall_info_mult, 1, 10);
+	if (rtsimc != rcu_task_stall_info_mult) {
+		pr_info("\tTasks-RCU CPU stall info multiplier clamped to %d (rcu_task_stall_info_mult).\n", rtsimc);
+		rcu_task_stall_info_mult = rtsimc;
+	}
 #endif /* #ifdef CONFIG_TASKS_RCU */
 #ifdef CONFIG_TASKS_RCU
 	pr_info("\tTrampoline variant of Tasks RCU enabled.\n");
@@ -568,7 +585,17 @@ static void __init rcu_tasks_bootup_oddness(void)
 /* Dump out rcutorture-relevant state common to all RCU-tasks flavors. */
 static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s)
 {
-	struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, 0); // for_each...
+	int cpu;
+	bool havecbs = false;
+
+	for_each_possible_cpu(cpu) {
+		struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu);
+
+		if (!data_race(rcu_segcblist_empty(&rtpcp->cblist))) {
+			havecbs = true;
+			break;
+		}
+	}
 	pr_info("%s: %s(%d) since %lu g:%lu i:%lu/%lu %c%c %s\n",
 		rtp->kname,
 		tasks_gp_state_getname(rtp), data_race(rtp->gp_state),
@@ -576,7 +603,7 @@ static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s)
 		data_race(rcu_seq_current(&rtp->tasks_gp_seq)),
 		data_race(rtp->n_ipis_fails), data_race(rtp->n_ipis),
 		".k"[!!data_race(rtp->kthread_ptr)],
-		".C"[!data_race(rcu_segcblist_empty(&rtpcp->cblist))],
+		".C"[havecbs],
 		s);
 }
 #endif // #ifndef CONFIG_TINY_RCU
@@ -592,10 +619,15 @@ static void exit_tasks_rcu_finish_trace(struct task_struct *t);
 /* Wait for one RCU-tasks grace period. */
 static void rcu_tasks_wait_gp(struct rcu_tasks *rtp)
 {
-	struct task_struct *g, *t;
+	struct task_struct *g;
-	unsigned long lastreport;
-	LIST_HEAD(holdouts);
 	int fract;
+	LIST_HEAD(holdouts);
+	unsigned long j;
+	unsigned long lastinfo;
+	unsigned long lastreport;
+	bool reported = false;
+	int rtsi;
+	struct task_struct *t;
 
 	set_tasks_gp_state(rtp, RTGS_PRE_WAIT_GP);
 	rtp->pregp_func();
@@ -621,30 +653,50 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp)
 	 * is empty, we are done.
 	 */
 	lastreport = jiffies;
+	lastinfo = lastreport;
+	rtsi = READ_ONCE(rcu_task_stall_info);
 
 	// Start off with initial wait and slowly back off to 1 HZ wait.
 	fract = rtp->init_fract;
 
 	while (!list_empty(&holdouts)) {
+		ktime_t exp;
 		bool firstreport;
 		bool needreport;
 		int rtst;
 
-		/* Slowly back off waiting for holdouts */
+		// Slowly back off waiting for holdouts
 		set_tasks_gp_state(rtp, RTGS_WAIT_SCAN_HOLDOUTS);
+		if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
 			schedule_timeout_idle(fract);
+		} else {
+			exp = jiffies_to_nsecs(fract);
+			__set_current_state(TASK_IDLE);
+			schedule_hrtimeout_range(&exp, jiffies_to_nsecs(HZ / 2), HRTIMER_MODE_REL_HARD);
+		}
 
 		if (fract < HZ)
 			fract++;
 
 		rtst = READ_ONCE(rcu_task_stall_timeout);
 		needreport = rtst > 0 && time_after(jiffies, lastreport + rtst);
-		if (needreport)
+		if (needreport) {
 			lastreport = jiffies;
+			reported = true;
+		}
 		firstreport = true;
 		WARN_ON(signal_pending(current));
 		set_tasks_gp_state(rtp, RTGS_SCAN_HOLDOUTS);
 		rtp->holdouts_func(&holdouts, needreport, &firstreport);
+
+		// Print pre-stall informational messages if needed.
+		j = jiffies;
+		if (rtsi > 0 && !reported && time_after(j, lastinfo + rtsi)) {
+			lastinfo = j;
+			rtsi = rtsi * rcu_task_stall_info_mult;
+			pr_info("%s: %s grace period %lu is %lu jiffies old.\n",
+				__func__, rtp->kname, rtp->tasks_gp_seq, j - rtp->gp_start);
+		}
 	}
 
 	set_tasks_gp_state(rtp, RTGS_POST_GP);
@@ -950,6 +1002,9 @@ static void rcu_tasks_be_rude(struct work_struct *work)
 // Wait for one rude RCU-tasks grace period.
 static void rcu_tasks_rude_wait_gp(struct rcu_tasks *rtp)
 {
+	if (num_online_cpus() <= 1)
+		return;	// Fastpath for only one CPU.
+
 	rtp->n_ipis += cpumask_weight(cpu_online_mask);
 	schedule_on_each_cpu(rcu_tasks_be_rude);
 }

kernel/rcu/tree.c

@@ -1679,6 +1679,8 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp)
 	rdp->gp_seq = rnp->gp_seq;  /* Remember new grace-period state. */
 	if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap)
 		WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);
+	if (IS_ENABLED(CONFIG_PROVE_RCU) && READ_ONCE(rdp->gpwrap))
+		WRITE_ONCE(rdp->last_sched_clock, jiffies);
 	WRITE_ONCE(rdp->gpwrap, false);
 	rcu_gpnum_ovf(rnp, rdp);
 	return ret;
@@ -1705,11 +1707,37 @@ static void note_gp_changes(struct rcu_data *rdp)
 		rcu_gp_kthread_wake();
 }
 
+static atomic_t *rcu_gp_slow_suppress;
+
+/* Register a counter to suppress debugging grace-period delays. */
+void rcu_gp_slow_register(atomic_t *rgssp)
+{
+	WARN_ON_ONCE(rcu_gp_slow_suppress);
+
+	WRITE_ONCE(rcu_gp_slow_suppress, rgssp);
+}
+EXPORT_SYMBOL_GPL(rcu_gp_slow_register);
+
+/* Unregister a counter, with NULL for not caring which. */
+void rcu_gp_slow_unregister(atomic_t *rgssp)
+{
+	WARN_ON_ONCE(rgssp && rgssp != rcu_gp_slow_suppress);
+
+	WRITE_ONCE(rcu_gp_slow_suppress, NULL);
+}
+EXPORT_SYMBOL_GPL(rcu_gp_slow_unregister);
+
+static bool rcu_gp_slow_is_suppressed(void)
+{
+	atomic_t *rgssp = READ_ONCE(rcu_gp_slow_suppress);
+
+	return rgssp && atomic_read(rgssp);
+}
+
 static void rcu_gp_slow(int delay)
 {
-	if (delay > 0 &&
+	if (!rcu_gp_slow_is_suppressed() && delay > 0 &&
-	    !(rcu_seq_ctr(rcu_state.gp_seq) %
+	    !(rcu_seq_ctr(rcu_state.gp_seq) % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
-	      (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
 		schedule_timeout_idle(delay);
 }
 
@@ -2096,14 +2124,29 @@ static noinline void rcu_gp_cleanup(void)
 	/* Advance CBs to reduce false positives below. */
 	offloaded = rcu_rdp_is_offloaded(rdp);
 	if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) {
+
+		// We get here if a grace period was needed (“needgp”)
+		// and the above call to rcu_accelerate_cbs() did not set
+		// the RCU_GP_FLAG_INIT bit in ->gp_state (which records
+		// the need for another grace period).  The purpose
+		// of the “offloaded” check is to avoid invoking
+		// rcu_accelerate_cbs() on an offloaded CPU because we do not
+		// hold the ->nocb_lock needed to safely access an offloaded
+		// ->cblist.  We do not want to acquire that lock because
+		// it can be heavily contended during callback floods.
+
 		WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT);
 		WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
-		trace_rcu_grace_period(rcu_state.name,
+		trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("newreq"));
-				       rcu_state.gp_seq,
-				       TPS("newreq"));
 	} else {
-		WRITE_ONCE(rcu_state.gp_flags,
+
-			   rcu_state.gp_flags & RCU_GP_FLAG_INIT);
+		// We get here either if there is no need for an
+		// additional grace period or if rcu_accelerate_cbs() has
+		// already set the RCU_GP_FLAG_INIT bit in ->gp_flags. 
+		// So all we need to do is to clear all of the other
+		// ->gp_flags bits.
+
+		WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags & RCU_GP_FLAG_INIT);
 	}
 	raw_spin_unlock_irq_rcu_node(rnp);
 
@@ -2609,6 +2652,13 @@ static void rcu_do_batch(struct rcu_data *rdp)
  */
 void rcu_sched_clock_irq(int user)
 {
+	unsigned long j;
+
+	if (IS_ENABLED(CONFIG_PROVE_RCU)) {
+		j = jiffies;
+		WARN_ON_ONCE(time_before(j, __this_cpu_read(rcu_data.last_sched_clock)));
+		__this_cpu_write(rcu_data.last_sched_clock, j);
+	}
 	trace_rcu_utilization(TPS("Start scheduler-tick"));
 	lockdep_assert_irqs_disabled();
 	raw_cpu_inc(rcu_data.ticks_this_gp);
@@ -2624,6 +2674,8 @@ void rcu_sched_clock_irq(int user)
 	rcu_flavor_sched_clock_irq(user);
 	if (rcu_pending(user))
 		invoke_rcu_core();
+	if (user)
+		rcu_tasks_classic_qs(current, false);
 	lockdep_assert_irqs_disabled();
 
 	trace_rcu_utilization(TPS("End scheduler-tick"));
@@ -3717,7 +3769,9 @@ static int rcu_blocking_is_gp(void)
 {
 	int ret;
 
-	if (IS_ENABLED(CONFIG_PREEMPTION))
+	// Invoking preempt_model_*() too early gets a splat.
+	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE ||
+	    preempt_model_full() || preempt_model_rt())
 		return rcu_scheduler_active == RCU_SCHEDULER_INACTIVE;
 	might_sleep();  /* Check for RCU read-side critical section. */
 	preempt_disable();
@@ -4179,6 +4233,7 @@ rcu_boot_init_percpu_data(int cpu)
 	rdp->rcu_ofl_gp_flags = RCU_GP_CLEANED;
 	rdp->rcu_onl_gp_seq = rcu_state.gp_seq;
 	rdp->rcu_onl_gp_flags = RCU_GP_CLEANED;
+	rdp->last_sched_clock = jiffies;
 	rdp->cpu = cpu;
 	rcu_boot_init_nocb_percpu_data(rdp);
 }
@@ -4471,6 +4526,51 @@ static int rcu_pm_notify(struct notifier_block *self,
 	return NOTIFY_OK;
 }
 
+#ifdef CONFIG_RCU_EXP_KTHREAD
+struct kthread_worker *rcu_exp_gp_kworker;
+struct kthread_worker *rcu_exp_par_gp_kworker;
+
+static void __init rcu_start_exp_gp_kworkers(void)
+{
+	const char *par_gp_kworker_name = "rcu_exp_par_gp_kthread_worker";
+	const char *gp_kworker_name = "rcu_exp_gp_kthread_worker";
+	struct sched_param param = { .sched_priority = kthread_prio };
+
+	rcu_exp_gp_kworker = kthread_create_worker(0, gp_kworker_name);
+	if (IS_ERR_OR_NULL(rcu_exp_gp_kworker)) {
+		pr_err("Failed to create %s!\n", gp_kworker_name);
+		return;
+	}
+
+	rcu_exp_par_gp_kworker = kthread_create_worker(0, par_gp_kworker_name);
+	if (IS_ERR_OR_NULL(rcu_exp_par_gp_kworker)) {
+		pr_err("Failed to create %s!\n", par_gp_kworker_name);
+		kthread_destroy_worker(rcu_exp_gp_kworker);
+		return;
+	}
+
+	sched_setscheduler_nocheck(rcu_exp_gp_kworker->task, SCHED_FIFO, &param);
+	sched_setscheduler_nocheck(rcu_exp_par_gp_kworker->task, SCHED_FIFO,
+				   &param);
+}
+
+static inline void rcu_alloc_par_gp_wq(void)
+{
+}
+#else /* !CONFIG_RCU_EXP_KTHREAD */
+struct workqueue_struct *rcu_par_gp_wq;
+
+static void __init rcu_start_exp_gp_kworkers(void)
+{
+}
+
+static inline void rcu_alloc_par_gp_wq(void)
+{
+	rcu_par_gp_wq = alloc_workqueue("rcu_par_gp", WQ_MEM_RECLAIM, 0);
+	WARN_ON(!rcu_par_gp_wq);
+}
+#endif /* CONFIG_RCU_EXP_KTHREAD */
+
 /*
  * Spawn the kthreads that handle RCU's grace periods.
  */
@@ -4480,6 +4580,7 @@ static int __init rcu_spawn_gp_kthread(void)
 	struct rcu_node *rnp;
 	struct sched_param sp;
 	struct task_struct *t;
+	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 
 	rcu_scheduler_fully_active = 1;
 	t = kthread_create(rcu_gp_kthread, NULL, "%s", rcu_state.name);
@@ -4497,9 +4598,17 @@ static int __init rcu_spawn_gp_kthread(void)
 	smp_store_release(&rcu_state.gp_kthread, t);  /* ^^^ */
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 	wake_up_process(t);
-	rcu_spawn_nocb_kthreads();
+	/* This is a pre-SMP initcall, we expect a single CPU */
-	rcu_spawn_boost_kthreads();
+	WARN_ON(num_online_cpus() > 1);
+	/*
+	 * Those kthreads couldn't be created on rcu_init() -> rcutree_prepare_cpu()
+	 * due to rcu_scheduler_fully_active.
+	 */
+	rcu_spawn_cpu_nocb_kthread(smp_processor_id());
+	rcu_spawn_one_boost_kthread(rdp->mynode);
 	rcu_spawn_core_kthreads();
+	/* Create kthread worker for expedited GPs */
+	rcu_start_exp_gp_kworkers();
 	return 0;
 }
 early_initcall(rcu_spawn_gp_kthread);
@@ -4745,7 +4854,6 @@ static void __init rcu_dump_rcu_node_tree(void)
 }
 
 struct workqueue_struct *rcu_gp_wq;
-struct workqueue_struct *rcu_par_gp_wq;
 
 static void __init kfree_rcu_batch_init(void)
 {
@@ -4782,7 +4890,7 @@ static void __init kfree_rcu_batch_init(void)
 
 void __init rcu_init(void)
 {
-	int cpu;
+	int cpu = smp_processor_id();
 
 	rcu_early_boot_tests();
 
@@ -4802,17 +4910,15 @@ void __init rcu_init(void)
 	 * or the scheduler are operational.
 	 */
 	pm_notifier(rcu_pm_notify, 0);
-	for_each_online_cpu(cpu) {
+	WARN_ON(num_online_cpus() > 1); // Only one CPU this early in boot.
 	rcutree_prepare_cpu(cpu);
 	rcu_cpu_starting(cpu);
 	rcutree_online_cpu(cpu);
-	}
 
 	/* Create workqueue for Tree SRCU and for expedited GPs. */
 	rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
 	WARN_ON(!rcu_gp_wq);
-	rcu_par_gp_wq = alloc_workqueue("rcu_par_gp", WQ_MEM_RECLAIM, 0);
+	rcu_alloc_par_gp_wq();
-	WARN_ON(!rcu_par_gp_wq);
 
 	/* Fill in default value for rcutree.qovld boot parameter. */
 	/* -After- the rcu_node ->lock fields are initialized! */

kernel/rcu/tree.h

@@ -10,6 +10,7 @@
  */
 
 #include <linux/cache.h>
+#include <linux/kthread.h>
 #include <linux/spinlock.h>
 #include <linux/rtmutex.h>
 #include <linux/threads.h>
@@ -23,7 +24,11 @@
 /* Communicate arguments to a workqueue handler. */
 struct rcu_exp_work {
 	unsigned long rew_s;
+#ifdef CONFIG_RCU_EXP_KTHREAD
+	struct kthread_work rew_work;
+#else
 	struct work_struct rew_work;
+#endif /* CONFIG_RCU_EXP_KTHREAD */
 };
 
 /* RCU's kthread states for tracing. */
@@ -254,6 +259,7 @@ struct rcu_data {
 	unsigned long rcu_onl_gp_seq;	/* ->gp_seq at last online. */
 	short rcu_onl_gp_flags;		/* ->gp_flags at last online. */
 	unsigned long last_fqs_resched;	/* Time of last rcu_resched(). */
+	unsigned long last_sched_clock;	/* Jiffies of last rcu_sched_clock_irq(). */
 
 	int cpu;
 };
@@ -364,6 +370,7 @@ struct rcu_state {
 	arch_spinlock_t ofl_lock ____cacheline_internodealigned_in_smp;
 						/* Synchronize offline with */
 						/*  GP pre-initialization. */
+	int nocb_is_setup;			/* nocb is setup from boot */
 };
 
 /* Values for rcu_state structure's gp_flags field. */
@@ -421,7 +428,6 @@ static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
 static bool rcu_is_callbacks_kthread(void);
 static void rcu_cpu_kthread_setup(unsigned int cpu);
 static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp);
-static void __init rcu_spawn_boost_kthreads(void);
 static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
 static bool rcu_preempt_need_deferred_qs(struct task_struct *t);
 static void rcu_preempt_deferred_qs(struct task_struct *t);
@@ -439,7 +445,6 @@ static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level);
 static bool do_nocb_deferred_wakeup(struct rcu_data *rdp);
 static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp);
 static void rcu_spawn_cpu_nocb_kthread(int cpu);
-static void __init rcu_spawn_nocb_kthreads(void);
 static void show_rcu_nocb_state(struct rcu_data *rdp);
 static void rcu_nocb_lock(struct rcu_data *rdp);
 static void rcu_nocb_unlock(struct rcu_data *rdp);

kernel/rcu/tree_exp.h

@@ -334,15 +334,13 @@ static bool exp_funnel_lock(unsigned long s)
  * Select the CPUs within the specified rcu_node that the upcoming
  * expedited grace period needs to wait for.
  */
-static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
+static void __sync_rcu_exp_select_node_cpus(struct rcu_exp_work *rewp)
 {
 	int cpu;
 	unsigned long flags;
 	unsigned long mask_ofl_test;
 	unsigned long mask_ofl_ipi;
 	int ret;
-	struct rcu_exp_work *rewp =
-		container_of(wp, struct rcu_exp_work, rew_work);
 	struct rcu_node *rnp = container_of(rewp, struct rcu_node, rew);
 
 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
@@ -417,13 +415,119 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
 		rcu_report_exp_cpu_mult(rnp, mask_ofl_test, false);
 }
 
+static void rcu_exp_sel_wait_wake(unsigned long s);
+
+#ifdef CONFIG_RCU_EXP_KTHREAD
+static void sync_rcu_exp_select_node_cpus(struct kthread_work *wp)
+{
+	struct rcu_exp_work *rewp =
+		container_of(wp, struct rcu_exp_work, rew_work);
+
+	__sync_rcu_exp_select_node_cpus(rewp);
+}
+
+static inline bool rcu_gp_par_worker_started(void)
+{
+	return !!READ_ONCE(rcu_exp_par_gp_kworker);
+}
+
+static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
+{
+	kthread_init_work(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
+	/*
+	 * Use rcu_exp_par_gp_kworker, because flushing a work item from
+	 * another work item on the same kthread worker can result in
+	 * deadlock.
+	 */
+	kthread_queue_work(rcu_exp_par_gp_kworker, &rnp->rew.rew_work);
+}
+
+static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp)
+{
+	kthread_flush_work(&rnp->rew.rew_work);
+}
+
+/*
+ * Work-queue handler to drive an expedited grace period forward.
+ */
+static void wait_rcu_exp_gp(struct kthread_work *wp)
+{
+	struct rcu_exp_work *rewp;
+
+	rewp = container_of(wp, struct rcu_exp_work, rew_work);
+	rcu_exp_sel_wait_wake(rewp->rew_s);
+}
+
+static inline void synchronize_rcu_expedited_queue_work(struct rcu_exp_work *rew)
+{
+	kthread_init_work(&rew->rew_work, wait_rcu_exp_gp);
+	kthread_queue_work(rcu_exp_gp_kworker, &rew->rew_work);
+}
+
+static inline void synchronize_rcu_expedited_destroy_work(struct rcu_exp_work *rew)
+{
+}
+#else /* !CONFIG_RCU_EXP_KTHREAD */
+static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
+{
+	struct rcu_exp_work *rewp =
+		container_of(wp, struct rcu_exp_work, rew_work);
+
+	__sync_rcu_exp_select_node_cpus(rewp);
+}
+
+static inline bool rcu_gp_par_worker_started(void)
+{
+	return !!READ_ONCE(rcu_par_gp_wq);
+}
+
+static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
+{
+	int cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1);
+
+	INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
+	/* If all offline, queue the work on an unbound CPU. */
+	if (unlikely(cpu > rnp->grphi - rnp->grplo))
+		cpu = WORK_CPU_UNBOUND;
+	else
+		cpu += rnp->grplo;
+	queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work);
+}
+
+static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp)
+{
+	flush_work(&rnp->rew.rew_work);
+}
+
+/*
+ * Work-queue handler to drive an expedited grace period forward.
+ */
+static void wait_rcu_exp_gp(struct work_struct *wp)
+{
+	struct rcu_exp_work *rewp;
+
+	rewp = container_of(wp, struct rcu_exp_work, rew_work);
+	rcu_exp_sel_wait_wake(rewp->rew_s);
+}
+
+static inline void synchronize_rcu_expedited_queue_work(struct rcu_exp_work *rew)
+{
+	INIT_WORK_ONSTACK(&rew->rew_work, wait_rcu_exp_gp);
+	queue_work(rcu_gp_wq, &rew->rew_work);
+}
+
+static inline void synchronize_rcu_expedited_destroy_work(struct rcu_exp_work *rew)
+{
+	destroy_work_on_stack(&rew->rew_work);
+}
+#endif /* CONFIG_RCU_EXP_KTHREAD */
+
 /*
  * Select the nodes that the upcoming expedited grace period needs
  * to wait for.
  */
 static void sync_rcu_exp_select_cpus(void)
 {
-	int cpu;
 	struct rcu_node *rnp;
 
 	trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("reset"));
@@ -435,28 +539,21 @@ static void sync_rcu_exp_select_cpus(void)
 		rnp->exp_need_flush = false;
 		if (!READ_ONCE(rnp->expmask))
 			continue; /* Avoid early boot non-existent wq. */
-		if (!READ_ONCE(rcu_par_gp_wq) ||
+		if (!rcu_gp_par_worker_started() ||
 		    rcu_scheduler_active != RCU_SCHEDULER_RUNNING ||
 		    rcu_is_last_leaf_node(rnp)) {
-			/* No workqueues yet or last leaf, do direct call. */
+			/* No worker started yet or last leaf, do direct call. */
 			sync_rcu_exp_select_node_cpus(&rnp->rew.rew_work);
 			continue;
 		}
-		INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
+		sync_rcu_exp_select_cpus_queue_work(rnp);
-		cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1);
-		/* If all offline, queue the work on an unbound CPU. */
-		if (unlikely(cpu > rnp->grphi - rnp->grplo))
-			cpu = WORK_CPU_UNBOUND;
-		else
-			cpu += rnp->grplo;
-		queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work);
 		rnp->exp_need_flush = true;
 	}
 
-	/* Wait for workqueue jobs (if any) to complete. */
+	/* Wait for jobs (if any) to complete. */
 	rcu_for_each_leaf_node(rnp)
 		if (rnp->exp_need_flush)
-			flush_work(&rnp->rew.rew_work);
+			sync_rcu_exp_select_cpus_flush_work(rnp);
 }
 
 /*
@@ -496,7 +593,7 @@ static void synchronize_rcu_expedited_wait(void)
 	struct rcu_node *rnp_root = rcu_get_root();
 
 	trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("startwait"));
-	jiffies_stall = rcu_jiffies_till_stall_check();
+	jiffies_stall = rcu_exp_jiffies_till_stall_check();
 	jiffies_start = jiffies;
 	if (tick_nohz_full_enabled() && rcu_inkernel_boot_has_ended()) {
 		if (synchronize_rcu_expedited_wait_once(1))
@@ -571,7 +668,7 @@ static void synchronize_rcu_expedited_wait(void)
 				dump_cpu_task(cpu);
 			}
 		}
-		jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3;
+		jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3;
 	}
 }
 
@@ -622,17 +719,6 @@ static void rcu_exp_sel_wait_wake(unsigned long s)
 	rcu_exp_wait_wake(s);
 }
 
-/*
- * Work-queue handler to drive an expedited grace period forward.
- */
-static void wait_rcu_exp_gp(struct work_struct *wp)
-{
-	struct rcu_exp_work *rewp;
-
-	rewp = container_of(wp, struct rcu_exp_work, rew_work);
-	rcu_exp_sel_wait_wake(rewp->rew_s);
-}
-
 #ifdef CONFIG_PREEMPT_RCU
 
 /*
@@ -848,20 +934,19 @@ void synchronize_rcu_expedited(void)
 	} else {
 		/* Marshall arguments & schedule the expedited grace period. */
 		rew.rew_s = s;
-		INIT_WORK_ONSTACK(&rew.rew_work, wait_rcu_exp_gp);
+		synchronize_rcu_expedited_queue_work(&rew);
-		queue_work(rcu_gp_wq, &rew.rew_work);
 	}
 
 	/* Wait for expedited grace period to complete. */
 	rnp = rcu_get_root();
 	wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
 		   sync_exp_work_done(s));
-	smp_mb(); /* Workqueue actions happen before return. */
+	smp_mb(); /* Work actions happen before return. */
 
 	/* Let the next expedited grace period start. */
 	mutex_unlock(&rcu_state.exp_mutex);
 
 	if (likely(!boottime))
-		destroy_work_on_stack(&rew.rew_work);
+		synchronize_rcu_expedited_destroy_work(&rew);
 }
 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);

kernel/rcu/tree_nocb.h

@@ -60,9 +60,6 @@ static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp)
  * Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters.
  * If the list is invalid, a warning is emitted and all CPUs are offloaded.
  */
-
-static bool rcu_nocb_is_setup;
-
 static int __init rcu_nocb_setup(char *str)
 {
 	alloc_bootmem_cpumask_var(&rcu_nocb_mask);
@@ -72,7 +69,7 @@ static int __init rcu_nocb_setup(char *str)
 			cpumask_setall(rcu_nocb_mask);
 		}
 	}
-	rcu_nocb_is_setup = true;
+	rcu_state.nocb_is_setup = true;
 	return 1;
 }
 __setup("rcu_nocbs", rcu_nocb_setup);
@@ -215,14 +212,6 @@ static void rcu_init_one_nocb(struct rcu_node *rnp)
 	init_swait_queue_head(&rnp->nocb_gp_wq[1]);
 }
 
-/* Is the specified CPU a no-CBs CPU? */
-bool rcu_is_nocb_cpu(int cpu)
-{
-	if (cpumask_available(rcu_nocb_mask))
-		return cpumask_test_cpu(cpu, rcu_nocb_mask);
-	return false;
-}
-
 static bool __wake_nocb_gp(struct rcu_data *rdp_gp,
 			   struct rcu_data *rdp,
 			   bool force, unsigned long flags)
@@ -1180,10 +1169,10 @@ void __init rcu_init_nohz(void)
 				return;
 			}
 		}
-		rcu_nocb_is_setup = true;
+		rcu_state.nocb_is_setup = true;
 	}
 
-	if (!rcu_nocb_is_setup)
+	if (!rcu_state.nocb_is_setup)
 		return;
 
 #if defined(CONFIG_NO_HZ_FULL)
@@ -1241,7 +1230,7 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu)
 	struct task_struct *t;
 	struct sched_param sp;
 
-	if (!rcu_scheduler_fully_active || !rcu_nocb_is_setup)
+	if (!rcu_scheduler_fully_active || !rcu_state.nocb_is_setup)
 		return;
 
 	/* If there already is an rcuo kthread, then nothing to do. */
@@ -1277,22 +1266,6 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu)
 	WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread);
 }
 
-/*
- * Once the scheduler is running, spawn rcuo kthreads for all online
- * no-CBs CPUs.  This assumes that the early_initcall()s happen before
- * non-boot CPUs come online -- if this changes, we will need to add
- * some mutual exclusion.
- */
-static void __init rcu_spawn_nocb_kthreads(void)
-{
-	int cpu;
-
-	if (rcu_nocb_is_setup) {
-		for_each_online_cpu(cpu)
-			rcu_spawn_cpu_nocb_kthread(cpu);
-	}
-}
-
 /* How many CB CPU IDs per GP kthread?  Default of -1 for sqrt(nr_cpu_ids). */
 static int rcu_nocb_gp_stride = -1;
 module_param(rcu_nocb_gp_stride, int, 0444);
@@ -1549,10 +1522,6 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu)
 {
 }
 
-static void __init rcu_spawn_nocb_kthreads(void)
-{
-}
-
 static void show_rcu_nocb_state(struct rcu_data *rdp)
 {
 }

kernel/rcu/tree_plugin.h

@@ -486,6 +486,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
 	t->rcu_read_unlock_special.s = 0;
 	if (special.b.need_qs) {
 		if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) {
+			rdp->cpu_no_qs.b.norm = false;
 			rcu_report_qs_rdp(rdp);
 			udelay(rcu_unlock_delay);
 		} else {
@@ -660,7 +661,13 @@ static void rcu_read_unlock_special(struct task_struct *t)
 			    expboost && !rdp->defer_qs_iw_pending && cpu_online(rdp->cpu)) {
 				// Get scheduler to re-evaluate and call hooks.
 				// If !IRQ_WORK, FQS scan will eventually IPI.
-				init_irq_work(&rdp->defer_qs_iw, rcu_preempt_deferred_qs_handler);
+				if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) &&
+				    IS_ENABLED(CONFIG_PREEMPT_RT))
+					rdp->defer_qs_iw = IRQ_WORK_INIT_HARD(
+								rcu_preempt_deferred_qs_handler);
+				else
+					init_irq_work(&rdp->defer_qs_iw,
+						      rcu_preempt_deferred_qs_handler);
 				rdp->defer_qs_iw_pending = true;
 				irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);
 			}
@@ -1124,7 +1131,8 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
 	__releases(rnp->lock)
 {
 	raw_lockdep_assert_held_rcu_node(rnp);
-	if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
+	if (!rnp->boost_kthread_task ||
+	    (!rcu_preempt_blocked_readers_cgp(rnp) && !rnp->exp_tasks)) {
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 		return;
 	}
@@ -1226,18 +1234,6 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
 	free_cpumask_var(cm);
 }
 
-/*
- * Spawn boost kthreads -- called as soon as the scheduler is running.
- */
-static void __init rcu_spawn_boost_kthreads(void)
-{
-	struct rcu_node *rnp;
-
-	rcu_for_each_leaf_node(rnp)
-		if (rcu_rnp_online_cpus(rnp))
-			rcu_spawn_one_boost_kthread(rnp);
-}
-
 #else /* #ifdef CONFIG_RCU_BOOST */
 
 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
@@ -1263,10 +1259,6 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
 {
 }
 
-static void __init rcu_spawn_boost_kthreads(void)
-{
-}
-
 #endif /* #else #ifdef CONFIG_RCU_BOOST */
 
 /*

kernel/rcu/tree_stall.h

@@ -25,6 +25,34 @@ int sysctl_max_rcu_stall_to_panic __read_mostly;
 #define RCU_STALL_MIGHT_DIV		8
 #define RCU_STALL_MIGHT_MIN		(2 * HZ)
 
+int rcu_exp_jiffies_till_stall_check(void)
+{
+	int cpu_stall_timeout = READ_ONCE(rcu_exp_cpu_stall_timeout);
+	int exp_stall_delay_delta = 0;
+	int till_stall_check;
+
+	// Zero says to use rcu_cpu_stall_timeout, but in milliseconds.
+	if (!cpu_stall_timeout)
+		cpu_stall_timeout = jiffies_to_msecs(rcu_jiffies_till_stall_check());
+
+	// Limit check must be consistent with the Kconfig limits for
+	// CONFIG_RCU_EXP_CPU_STALL_TIMEOUT, so check the allowed range.
+	// The minimum clamped value is "2UL", because at least one full
+	// tick has to be guaranteed.
+	till_stall_check = clamp(msecs_to_jiffies(cpu_stall_timeout), 2UL, 21UL * HZ);
+
+	if (cpu_stall_timeout && jiffies_to_msecs(till_stall_check) != cpu_stall_timeout)
+		WRITE_ONCE(rcu_exp_cpu_stall_timeout, jiffies_to_msecs(till_stall_check));
+
+#ifdef CONFIG_PROVE_RCU
+	/* Add extra ~25% out of till_stall_check. */
+	exp_stall_delay_delta = ((till_stall_check * 25) / 100) + 1;
+#endif
+
+	return till_stall_check + exp_stall_delay_delta;
+}
+EXPORT_SYMBOL_GPL(rcu_exp_jiffies_till_stall_check);
+
 /* Limit-check stall timeouts specified at boottime and runtime. */
 int rcu_jiffies_till_stall_check(void)
 {
@@ -565,9 +593,9 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
 
 	for_each_possible_cpu(cpu)
 		totqlen += rcu_get_n_cbs_cpu(cpu);
-	pr_cont("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n",
+	pr_cont("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu ncpus=%d)\n",
 	       smp_processor_id(), (long)(jiffies - gps),
-	       (long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
+	       (long)rcu_seq_current(&rcu_state.gp_seq), totqlen, rcu_state.n_online_cpus);
 	if (ndetected) {
 		rcu_dump_cpu_stacks();
 
@@ -626,9 +654,9 @@ static void print_cpu_stall(unsigned long gps)
 	raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags);
 	for_each_possible_cpu(cpu)
 		totqlen += rcu_get_n_cbs_cpu(cpu);
-	pr_cont("\t(t=%lu jiffies g=%ld q=%lu)\n",
+	pr_cont("\t(t=%lu jiffies g=%ld q=%lu ncpus=%d)\n",
 		jiffies - gps,
-		(long)rcu_seq_current(&rcu_state.gp_seq), totqlen);
+		(long)rcu_seq_current(&rcu_state.gp_seq), totqlen, rcu_state.n_online_cpus);
 
 	rcu_check_gp_kthread_expired_fqs_timer();
 	rcu_check_gp_kthread_starvation();

kernel/rcu/update.c

@@ -506,6 +506,8 @@ EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress);
 module_param(rcu_cpu_stall_suppress, int, 0644);
 int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
 module_param(rcu_cpu_stall_timeout, int, 0644);
+int rcu_exp_cpu_stall_timeout __read_mostly = CONFIG_RCU_EXP_CPU_STALL_TIMEOUT;
+module_param(rcu_exp_cpu_stall_timeout, int, 0644);
 #endif /* #ifdef CONFIG_RCU_STALL_COMMON */
 
 // Suppress boot-time RCU CPU stall warnings and rcutorture writer stall

kernel/scftorture.c

@@ -267,10 +267,11 @@ static void scf_handler(void *scfc_in)
 	}
 	this_cpu_inc(scf_invoked_count);
 	if (longwait <= 0) {
-		if (!(r & 0xffc0))
+		if (!(r & 0xffc0)) {
 			udelay(r & 0x3f);
 			goto out;
 		}
+	}
 	if (r & 0xfff)
 		goto out;
 	r = (r >> 12);

kernel/sched/core.c

@@ -8415,6 +8415,18 @@ static void __init preempt_dynamic_init(void)
 	}
 }
 
+#define PREEMPT_MODEL_ACCESSOR(mode) \
+	bool preempt_model_##mode(void)						 \
+	{									 \
+		WARN_ON_ONCE(preempt_dynamic_mode == preempt_dynamic_undefined); \
+		return preempt_dynamic_mode == preempt_dynamic_##mode;		 \
+	}									 \
+	EXPORT_SYMBOL_GPL(preempt_model_##mode)
+
+PREEMPT_MODEL_ACCESSOR(none);
+PREEMPT_MODEL_ACCESSOR(voluntary);
+PREEMPT_MODEL_ACCESSOR(full);
+
 #else /* !CONFIG_PREEMPT_DYNAMIC */
 
 static inline void preempt_dynamic_init(void) { }

kernel/smp.c

@@ -183,7 +183,9 @@ static DEFINE_PER_CPU(smp_call_func_t, cur_csd_func);
 static DEFINE_PER_CPU(void *, cur_csd_info);
 static DEFINE_PER_CPU(struct cfd_seq_local, cfd_seq_local);
 
-#define CSD_LOCK_TIMEOUT (5ULL * NSEC_PER_SEC)
+static ulong csd_lock_timeout = 5000;  /* CSD lock timeout in milliseconds. */
+module_param(csd_lock_timeout, ulong, 0444);
+
 static atomic_t csd_bug_count = ATOMIC_INIT(0);
 static u64 cfd_seq;
 
@@ -329,6 +331,7 @@ static bool csd_lock_wait_toolong(struct __call_single_data *csd, u64 ts0, u64 *
 	u64 ts2, ts_delta;
 	call_single_data_t *cpu_cur_csd;
 	unsigned int flags = READ_ONCE(csd->node.u_flags);
+	unsigned long long csd_lock_timeout_ns = csd_lock_timeout * NSEC_PER_MSEC;
 
 	if (!(flags & CSD_FLAG_LOCK)) {
 		if (!unlikely(*bug_id))
@@ -341,7 +344,7 @@ static bool csd_lock_wait_toolong(struct __call_single_data *csd, u64 ts0, u64 *
 
 	ts2 = sched_clock();
 	ts_delta = ts2 - *ts1;
-	if (likely(ts_delta <= CSD_LOCK_TIMEOUT))
+	if (likely(ts_delta <= csd_lock_timeout_ns || csd_lock_timeout_ns == 0))
 		return false;
 
 	firsttime = !*bug_id;

kernel/trace/Kconfig

@@ -144,6 +144,7 @@ config TRACING
 	select BINARY_PRINTF
 	select EVENT_TRACING
 	select TRACE_CLOCK
+	select TASKS_RCU if PREEMPTION
 
 config GENERIC_TRACER
 	bool

tools/testing/selftests/rcutorture/bin/functions.sh

@@ -301,7 +301,7 @@ specify_qemu_cpus () {
 			echo $2 -smp $3
 			;;
 		qemu-system-ppc64)
-			nt="`lscpu | grep '^NUMA node0' | sed -e 's/^[^,]*,\([0-9]*\),.*$/\1/'`"
+			nt="`lscpu | sed -n 's/^Thread(s) per core:\s*//p'`"
 			echo $2 -smp cores=`expr \( $3 + $nt - 1 \) / $nt`,threads=$nt
 			;;
 		esac

tools/testing/selftests/rcutorture/bin/kvm-find-errors.sh

@@ -36,7 +36,7 @@ do
 	then
 		egrep "error:|warning:|^ld: .*undefined reference to" < $i > $i.diags
 		files="$files $i.diags $i"
-	elif ! test -f ${scenariobasedir}/vmlinux
+	elif ! test -f ${scenariobasedir}/vmlinux && ! test -f "${rundir}/re-run"
 	then
 		echo No ${scenariobasedir}/vmlinux file > $i.diags
 		files="$files $i.diags $i"

tools/testing/selftests/rcutorture/bin/kvm-recheck.sh

@@ -33,7 +33,12 @@ do
 		TORTURE_SUITE="`cat $i/../torture_suite`"
 		configfile=`echo $i | sed -e 's,^.*/,,'`
 		rm -f $i/console.log.*.diags
+		case "${TORTURE_SUITE}" in
+		X*)
+			;;
+		*)
 			kvm-recheck-${TORTURE_SUITE}.sh $i
+		esac
 		if test -f "$i/qemu-retval" && test "`cat $i/qemu-retval`" -ne 0 && test "`cat $i/qemu-retval`" -ne 137
 		then
 			echo QEMU error, output:

tools/testing/selftests/rcutorture/bin/kvm-remote.sh

@@ -138,14 +138,14 @@ chmod +x $T/bin/kvm-remote-*.sh
 # Check first to avoid the need for cleanup for system-name typos
 for i in $systems
 do
-	ncpus="`ssh $i getconf _NPROCESSORS_ONLN 2> /dev/null`"
+	ncpus="`ssh -o BatchMode=yes $i getconf _NPROCESSORS_ONLN 2> /dev/null`"
-	echo $i: $ncpus CPUs " " `date` | tee -a "$oldrun/remote-log"
 	ret=$?
 	if test "$ret" -ne 0
 	then
 		echo System $i unreachable, giving up. | tee -a "$oldrun/remote-log"
 		exit 4
 	fi
+	echo $i: $ncpus CPUs " " `date` | tee -a "$oldrun/remote-log"
 done
 
 # Download and expand the tarball on all systems.
@@ -153,14 +153,14 @@ echo Build-products tarball: `du -h $T/binres.tgz` | tee -a "$oldrun/remote-log"
 for i in $systems
 do
 	echo Downloading tarball to $i `date` | tee -a "$oldrun/remote-log"
-	cat $T/binres.tgz | ssh $i "cd /tmp; tar -xzf -"
+	cat $T/binres.tgz | ssh -o BatchMode=yes $i "cd /tmp; tar -xzf -"
 	ret=$?
 	tries=0
 	while test "$ret" -ne 0
 	do
 		echo Unable to download $T/binres.tgz to system $i, waiting and then retrying.  $tries prior retries. | tee -a "$oldrun/remote-log"
 		sleep 60
-		cat $T/binres.tgz | ssh $i "cd /tmp; tar -xzf -"
+		cat $T/binres.tgz | ssh -o BatchMode=yes $i "cd /tmp; tar -xzf -"
 		ret=$?
 		if test "$ret" -ne 0
 		then
@@ -185,7 +185,7 @@ checkremotefile () {
 
 	while :
 	do
-		ssh $1 "test -f \"$2\""
+		ssh -o BatchMode=yes $1 "test -f \"$2\""
 		ret=$?
 		if test "$ret" -eq 255
 		then
@@ -228,7 +228,7 @@ startbatches () {
 		then
 			continue # System still running last test, skip.
 		fi
-		ssh "$i" "cd \"$resdir/$ds\"; touch remote.run; PATH=\"$T/bin:$PATH\" nohup kvm-remote-$curbatch.sh > kvm-remote-$curbatch.sh.out 2>&1 &" 1>&2
+		ssh -o BatchMode=yes "$i" "cd \"$resdir/$ds\"; touch remote.run; PATH=\"$T/bin:$PATH\" nohup kvm-remote-$curbatch.sh > kvm-remote-$curbatch.sh.out 2>&1 &" 1>&2
 		ret=$?
 		if test "$ret" -ne 0
 		then
@@ -267,7 +267,7 @@ do
 		sleep 30
 	done
 	echo " ---" Collecting results from $i `date` | tee -a "$oldrun/remote-log"
-	( cd "$oldrun"; ssh $i "cd $rundir; tar -czf - kvm-remote-*.sh.out */console.log */kvm-test-1-run*.sh.out */qemu[_-]pid */qemu-retval */qemu-affinity; rm -rf $T > /dev/null 2>&1" | tar -xzf - )
+	( cd "$oldrun"; ssh -o BatchMode=yes $i "cd $rundir; tar -czf - kvm-remote-*.sh.out */console.log */kvm-test-1-run*.sh.out */qemu[_-]pid */qemu-retval */qemu-affinity; rm -rf $T > /dev/null 2>&1" | tar -xzf - )
 done
 
 ( kvm-end-run-stats.sh "$oldrun" "$starttime"; echo $? > $T/exitcode ) | tee -a "$oldrun/remote-log"

tools/testing/selftests/rcutorture/bin/kvm.sh

@@ -44,6 +44,7 @@ TORTURE_KCONFIG_KASAN_ARG=""
 TORTURE_KCONFIG_KCSAN_ARG=""
 TORTURE_KMAKE_ARG=""
 TORTURE_QEMU_MEM=512
+torture_qemu_mem_default=1
 TORTURE_REMOTE=
 TORTURE_SHUTDOWN_GRACE=180
 TORTURE_SUITE=rcu
@@ -86,7 +87,7 @@ usage () {
 	echo "       --remote"
 	echo "       --results absolute-pathname"
 	echo "       --shutdown-grace seconds"
-	echo "       --torture lock|rcu|rcuscale|refscale|scf"
+	echo "       --torture lock|rcu|rcuscale|refscale|scf|X*"
 	echo "       --trust-make"
 	exit 1
 }
@@ -180,6 +181,10 @@ do
 		;;
 	--kasan)
 		TORTURE_KCONFIG_KASAN_ARG="CONFIG_DEBUG_INFO=y CONFIG_KASAN=y"; export TORTURE_KCONFIG_KASAN_ARG
+		if test -n "$torture_qemu_mem_default"
+		then
+			TORTURE_QEMU_MEM=2G
+		fi
 		;;
 	--kconfig|--kconfigs)
 		checkarg --kconfig "(Kconfig options)" $# "$2" '^CONFIG_[A-Z0-9_]\+=\([ynm]\|[0-9]\+\)\( CONFIG_[A-Z0-9_]\+=\([ynm]\|[0-9]\+\)\)*$' '^error$'
@@ -202,6 +207,7 @@ do
 	--memory)
 		checkarg --memory "(memory size)" $# "$2" '^[0-9]\+[MG]\?$' error
 		TORTURE_QEMU_MEM=$2
+		torture_qemu_mem_default=
 		shift
 		;;
 	--no-initrd)
@@ -231,7 +237,7 @@ do
 		shift
 		;;
 	--torture)
-		checkarg --torture "(suite name)" "$#" "$2" '^\(lock\|rcu\|rcuscale\|refscale\|scf\)$' '^--'
+		checkarg --torture "(suite name)" "$#" "$2" '^\(lock\|rcu\|rcuscale\|refscale\|scf\|X.*\)$' '^--'
 		TORTURE_SUITE=$2
 		TORTURE_MOD="`echo $TORTURE_SUITE | sed -e 's/^\(lock\|rcu\|scf\)$/\1torture/'`"
 		shift

tools/testing/selftests/rcutorture/bin/torture.sh

@@ -54,6 +54,7 @@ do_kvfree=yes
 do_kasan=yes
 do_kcsan=no
 do_clocksourcewd=yes
+do_rt=yes
 
 # doyesno - Helper function for yes/no arguments
 function doyesno () {
@@ -82,6 +83,7 @@ usage () {
 	echo "       --do-rcuscale / --do-no-rcuscale"
 	echo "       --do-rcutorture / --do-no-rcutorture"
 	echo "       --do-refscale / --do-no-refscale"
+	echo "       --do-rt / --do-no-rt"
 	echo "       --do-scftorture / --do-no-scftorture"
 	echo "       --duration [ <minutes> | <hours>h | <days>d ]"
 	echo "       --kcsan-kmake-arg kernel-make-arguments"
@@ -118,6 +120,7 @@ do
 		do_scftorture=yes
 		do_rcuscale=yes
 		do_refscale=yes
+		do_rt=yes
 		do_kvfree=yes
 		do_kasan=yes
 		do_kcsan=yes
@@ -148,6 +151,7 @@ do
 		do_scftorture=no
 		do_rcuscale=no
 		do_refscale=no
+		do_rt=no
 		do_kvfree=no
 		do_kasan=no
 		do_kcsan=no
@@ -162,6 +166,9 @@ do
 	--do-refscale|--do-no-refscale)
 		do_refscale=`doyesno "$1" --do-refscale`
 		;;
+	--do-rt|--do-no-rt)
+		do_rt=`doyesno "$1" --do-rt`
+		;;
 	--do-scftorture|--do-no-scftorture)
 		do_scftorture=`doyesno "$1" --do-scftorture`
 		;;
@@ -322,6 +329,7 @@ then
 	echo " --- make clean" > "$amcdir/Make.out" 2>&1
 	make -j$MAKE_ALLOTED_CPUS clean >> "$amcdir/Make.out" 2>&1
 	echo " --- make allmodconfig" >> "$amcdir/Make.out" 2>&1
+	cp .config $amcdir
 	make -j$MAKE_ALLOTED_CPUS allmodconfig >> "$amcdir/Make.out" 2>&1
 	echo " --- make " >> "$amcdir/Make.out" 2>&1
 	make -j$MAKE_ALLOTED_CPUS >> "$amcdir/Make.out" 2>&1
@@ -350,8 +358,19 @@ fi
 
 if test "$do_scftorture" = "yes"
 then
-	torture_bootargs="scftorture.nthreads=$HALF_ALLOTED_CPUS torture.disable_onoff_at_boot"
+	torture_bootargs="scftorture.nthreads=$HALF_ALLOTED_CPUS torture.disable_onoff_at_boot csdlock_debug=1"
-	torture_set "scftorture" tools/testing/selftests/rcutorture/bin/kvm.sh --torture scf --allcpus --duration "$duration_scftorture" --configs "$configs_scftorture" --kconfig "CONFIG_NR_CPUS=$HALF_ALLOTED_CPUS" --memory 1G --trust-make
+	torture_set "scftorture" tools/testing/selftests/rcutorture/bin/kvm.sh --torture scf --allcpus --duration "$duration_scftorture" --configs "$configs_scftorture" --kconfig "CONFIG_NR_CPUS=$HALF_ALLOTED_CPUS" --memory 2G --trust-make
+fi
+
+if test "$do_rt" = "yes"
+then
+	# With all post-boot grace periods forced to normal.
+	torture_bootargs="rcupdate.rcu_cpu_stall_suppress_at_boot=1 torture.disable_onoff_at_boot rcupdate.rcu_task_stall_timeout=30000 rcupdate.rcu_normal=1"
+	torture_set "rcurttorture" tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration "$duration_rcutorture" --configs "TREE03" --trust-make
+
+	# With all post-boot grace periods forced to expedited.
+	torture_bootargs="rcupdate.rcu_cpu_stall_suppress_at_boot=1 torture.disable_onoff_at_boot rcupdate.rcu_task_stall_timeout=30000 rcupdate.rcu_expedited=1"
+	torture_set "rcurttorture-exp" tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration "$duration_rcutorture" --configs "TREE03" --trust-make
 fi
 
 if test "$do_refscale" = yes
@@ -363,7 +382,7 @@ fi
 for prim in $primlist
 do
 	torture_bootargs="refscale.scale_type="$prim" refscale.nreaders=$HALF_ALLOTED_CPUS refscale.loops=10000 refscale.holdoff=20 torture.disable_onoff_at_boot"
-	torture_set "refscale-$prim" tools/testing/selftests/rcutorture/bin/kvm.sh --torture refscale --allcpus --duration 5 --kconfig "CONFIG_NR_CPUS=$HALF_ALLOTED_CPUS" --bootargs "verbose_batched=$VERBOSE_BATCH_CPUS torture.verbose_sleep_frequency=8 torture.verbose_sleep_duration=$VERBOSE_BATCH_CPUS" --trust-make
+	torture_set "refscale-$prim" tools/testing/selftests/rcutorture/bin/kvm.sh --torture refscale --allcpus --duration 5 --kconfig "CONFIG_TASKS_TRACE_RCU=y CONFIG_NR_CPUS=$HALF_ALLOTED_CPUS" --bootargs "verbose_batched=$VERBOSE_BATCH_CPUS torture.verbose_sleep_frequency=8 torture.verbose_sleep_duration=$VERBOSE_BATCH_CPUS" --trust-make
 done
 
 if test "$do_rcuscale" = yes
@@ -375,13 +394,13 @@ fi
 for prim in $primlist
 do
 	torture_bootargs="rcuscale.scale_type="$prim" rcuscale.nwriters=$HALF_ALLOTED_CPUS rcuscale.holdoff=20 torture.disable_onoff_at_boot"
-	torture_set "rcuscale-$prim" tools/testing/selftests/rcutorture/bin/kvm.sh --torture rcuscale --allcpus --duration 5 --kconfig "CONFIG_NR_CPUS=$HALF_ALLOTED_CPUS" --trust-make
+	torture_set "rcuscale-$prim" tools/testing/selftests/rcutorture/bin/kvm.sh --torture rcuscale --allcpus --duration 5 --kconfig "CONFIG_TASKS_TRACE_RCU=y CONFIG_NR_CPUS=$HALF_ALLOTED_CPUS" --trust-make
 done
 
 if test "$do_kvfree" = "yes"
 then
 	torture_bootargs="rcuscale.kfree_rcu_test=1 rcuscale.kfree_nthreads=16 rcuscale.holdoff=20 rcuscale.kfree_loops=10000 torture.disable_onoff_at_boot"
-	torture_set "rcuscale-kvfree" tools/testing/selftests/rcutorture/bin/kvm.sh --torture rcuscale --allcpus --duration 10 --kconfig "CONFIG_NR_CPUS=$HALF_ALLOTED_CPUS" --memory 1G --trust-make
+	torture_set "rcuscale-kvfree" tools/testing/selftests/rcutorture/bin/kvm.sh --torture rcuscale --allcpus --duration 10 --kconfig "CONFIG_NR_CPUS=$HALF_ALLOTED_CPUS" --memory 2G --trust-make
 fi
 
 if test "$do_clocksourcewd" = "yes"

tools/testing/selftests/rcutorture/configs/rcu/RUDE01

@@ -8,3 +8,5 @@ CONFIG_DEBUG_LOCK_ALLOC=y
 CONFIG_PROVE_LOCKING=y
 #CHECK#CONFIG_PROVE_RCU=y
 CONFIG_RCU_EXPERT=y
+CONFIG_FORCE_TASKS_RUDE_RCU=y
+#CHECK#CONFIG_TASKS_RUDE_RCU=y

tools/testing/selftests/rcutorture/configs/rcu/SRCU-N

@@ -6,3 +6,5 @@ CONFIG_PREEMPT_NONE=y
 CONFIG_PREEMPT_VOLUNTARY=n
 CONFIG_PREEMPT=n
 #CHECK#CONFIG_RCU_EXPERT=n
+CONFIG_KPROBES=n
+CONFIG_FTRACE=n

tools/testing/selftests/rcutorture/configs/rcu/TASKS01

@@ -7,4 +7,5 @@ CONFIG_PREEMPT=y
 CONFIG_DEBUG_LOCK_ALLOC=y
 CONFIG_PROVE_LOCKING=y
 #CHECK#CONFIG_PROVE_RCU=y
+CONFIG_TASKS_RCU=y
 CONFIG_RCU_EXPERT=y

tools/testing/selftests/rcutorture/configs/rcu/TASKS02

@@ -2,3 +2,7 @@ CONFIG_SMP=n
 CONFIG_PREEMPT_NONE=y
 CONFIG_PREEMPT_VOLUNTARY=n
 CONFIG_PREEMPT=n
+CONFIG_PREEMPT_DYNAMIC=n
+#CHECK#CONFIG_TASKS_RCU=y
+CONFIG_FORCE_TASKS_RCU=y
+CONFIG_RCU_EXPERT=y

tools/testing/selftests/rcutorture/configs/rcu/TASKS02.boot

@@ -1 +1,2 @@
 rcutorture.torture_type=tasks
+rcutorture.stat_interval=60

tools/testing/selftests/rcutorture/configs/rcu/TASKS03

@@ -7,3 +7,5 @@ CONFIG_HZ_PERIODIC=n
 CONFIG_NO_HZ_IDLE=n
 CONFIG_NO_HZ_FULL=y
 #CHECK#CONFIG_RCU_EXPERT=n
+CONFIG_TASKS_RCU=y
+CONFIG_RCU_EXPERT=y

tools/testing/selftests/rcutorture/configs/rcu/TRACE01

@@ -4,8 +4,11 @@ CONFIG_HOTPLUG_CPU=y
 CONFIG_PREEMPT_NONE=y
 CONFIG_PREEMPT_VOLUNTARY=n
 CONFIG_PREEMPT=n
+CONFIG_PREEMPT_DYNAMIC=n
 CONFIG_DEBUG_LOCK_ALLOC=n
 CONFIG_PROVE_LOCKING=n
 #CHECK#CONFIG_PROVE_RCU=n
+CONFIG_FORCE_TASKS_TRACE_RCU=y
+#CHECK#CONFIG_TASKS_TRACE_RCU=y
 CONFIG_TASKS_TRACE_RCU_READ_MB=y
 CONFIG_RCU_EXPERT=y

tools/testing/selftests/rcutorture/configs/rcu/TRACE02

@@ -7,5 +7,7 @@ CONFIG_PREEMPT=y
 CONFIG_DEBUG_LOCK_ALLOC=y
 CONFIG_PROVE_LOCKING=y
 #CHECK#CONFIG_PROVE_RCU=y
+CONFIG_FORCE_TASKS_TRACE_RCU=y
+#CHECK#CONFIG_TASKS_TRACE_RCU=y
 CONFIG_TASKS_TRACE_RCU_READ_MB=n
 CONFIG_RCU_EXPERT=y

tools/testing/selftests/rcutorture/configs/rcu/TREE04

@@ -1,8 +1,9 @@
 CONFIG_SMP=y
 CONFIG_NR_CPUS=8
-CONFIG_PREEMPT_NONE=y
+CONFIG_PREEMPT_NONE=n
-CONFIG_PREEMPT_VOLUNTARY=n
+CONFIG_PREEMPT_VOLUNTARY=y
 CONFIG_PREEMPT=n
+CONFIG_PREEMPT_DYNAMIC=n
 #CHECK#CONFIG_TREE_RCU=y
 CONFIG_HZ_PERIODIC=n
 CONFIG_NO_HZ_IDLE=n

tools/testing/selftests/rcutorture/configs/rcu/TREE07

@@ -3,6 +3,7 @@ CONFIG_NR_CPUS=16
 CONFIG_PREEMPT_NONE=y
 CONFIG_PREEMPT_VOLUNTARY=n
 CONFIG_PREEMPT=n
+CONFIG_PREEMPT_DYNAMIC=n
 #CHECK#CONFIG_TREE_RCU=y
 CONFIG_HZ_PERIODIC=n
 CONFIG_NO_HZ_IDLE=n

tools/testing/selftests/rcutorture/configs/rcu/TREE09

@@ -13,3 +13,5 @@ CONFIG_DEBUG_LOCK_ALLOC=n
 CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 #CHECK#CONFIG_RCU_EXPERT=n
+CONFIG_KPROBES=n
+CONFIG_FTRACE=n

tools/testing/selftests/rcutorture/configs/rcu/TREE10

@@ -3,6 +3,7 @@ CONFIG_NR_CPUS=56
 CONFIG_PREEMPT_NONE=y
 CONFIG_PREEMPT_VOLUNTARY=n
 CONFIG_PREEMPT=n
+CONFIG_PREEMPT_DYNAMIC=n
 #CHECK#CONFIG_TREE_RCU=y
 CONFIG_HZ_PERIODIC=n
 CONFIG_NO_HZ_IDLE=y

tools/testing/selftests/rcutorture/configs/rcu/ver_functions.sh

@@ -9,7 +9,7 @@
 
 # rcutorture_param_n_barrier_cbs bootparam-string
 #
-# Adds n_barrier_cbs rcutorture module parameter to kernels having it.
+# Adds n_barrier_cbs rcutorture module parameter if not already specified.
 rcutorture_param_n_barrier_cbs () {
 	if echo $1 | grep -q "rcutorture\.n_barrier_cbs"
 	then
@@ -30,13 +30,25 @@ rcutorture_param_onoff () {
 	fi
 }
 
+# rcutorture_param_stat_interval bootparam-string
+#
+# Adds stat_interval rcutorture module parameter if not already specified.
+rcutorture_param_stat_interval () {
+	if echo $1 | grep -q "rcutorture\.stat_interval"
+	then
+		:
+	else
+		echo rcutorture.stat_interval=15
+	fi
+}
+
 # per_version_boot_params bootparam-string config-file seconds
 #
 # Adds per-version torture-module parameters to kernels supporting them.
 per_version_boot_params () {
 	echo $1 `rcutorture_param_onoff "$1" "$2"` \
 		`rcutorture_param_n_barrier_cbs "$1"` \
-		rcutorture.stat_interval=15 \
+		`rcutorture_param_stat_interval "$1"` \
 		rcutorture.shutdown_secs=$3 \
 		rcutorture.test_no_idle_hz=1 \
 		rcutorture.verbose=1

tools/testing/selftests/rcutorture/configs/rcuscale/CFcommon

@@ -1,5 +1,6 @@
 CONFIG_RCU_SCALE_TEST=y
 CONFIG_PRINTK_TIME=y
-CONFIG_TASKS_RCU_GENERIC=y
+CONFIG_FORCE_TASKS_RCU=y
-CONFIG_TASKS_RCU=y
+#CHECK#CONFIG_TASKS_RCU=y
-CONFIG_TASKS_TRACE_RCU=y
+CONFIG_FORCE_TASKS_TRACE_RCU=y
+#CHECK#CONFIG_TASKS_TRACE_RCU=y

tools/testing/selftests/rcutorture/configs/rcuscale/TREE

@@ -16,3 +16,5 @@ CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y
 CONFIG_RCU_TRACE=y
+CONFIG_KPROBES=n
+CONFIG_FTRACE=n

tools/testing/selftests/rcutorture/configs/refscale/CFcommon

@@ -1,2 +1,6 @@
 CONFIG_RCU_REF_SCALE_TEST=y
 CONFIG_PRINTK_TIME=y
+CONFIG_FORCE_TASKS_RCU=y
+#CHECK#CONFIG_TASKS_RCU=y
+CONFIG_FORCE_TASKS_TRACE_RCU=y
+#CHECK#CONFIG_TASKS_TRACE_RCU=y

tools/testing/selftests/rcutorture/configs/refscale/NOPREEMPT

@@ -15,3 +15,5 @@ CONFIG_PROVE_LOCKING=n
 CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y
+CONFIG_KPROBES=n
+CONFIG_FTRACE=n

tools/testing/selftests/rcutorture/configs/scf/NOPREEMPT

@@ -7,3 +7,5 @@ CONFIG_NO_HZ_IDLE=n
 CONFIG_NO_HZ_FULL=y
 CONFIG_DEBUG_LOCK_ALLOC=n
 CONFIG_PROVE_LOCKING=n
+CONFIG_KPROBES=n
+CONFIG_FTRACE=n

tools/testing/selftests/rcutorture/configs/scf/PREEMPT

@@ -7,3 +7,4 @@ CONFIG_NO_HZ_IDLE=y
 CONFIG_NO_HZ_FULL=n
 CONFIG_DEBUG_LOCK_ALLOC=y
 CONFIG_PROVE_LOCKING=y
+CONFIG_RCU_EXPERT=y

tools/testing/selftests/rcutorture/configs/scf/ver_functions.sh

@@ -25,6 +25,5 @@ per_version_boot_params () {
 	echo $1 `scftorture_param_onoff "$1" "$2"` \
 		scftorture.stat_interval=15 \
 		scftorture.shutdown_secs=$3 \
-		scftorture.verbose=1 \
+		scftorture.verbose=1
-		scf
 }