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Konstantin Khlebnikov 6284d30e96 clocksource: Prevent double add_timer_on() for watchdog_timer commit `febac332a8` upstream. Kernel crashes inside QEMU/KVM are observed: kernel BUG at kernel/time/timer.c:1154! BUG_ON(timer_pending(timer) \|\| !timer->function) in add_timer_on(). At the same time another cpu got: general protection fault: 0000 [#1] SMP PTI of poinson pointer 0xdead000000000200 in: __hlist_del at include/linux/list.h:681 (inlined by) detach_timer at kernel/time/timer.c:818 (inlined by) expire_timers at kernel/time/timer.c:1355 (inlined by) __run_timers at kernel/time/timer.c:1686 (inlined by) run_timer_softirq at kernel/time/timer.c:1699 Unfortunately kernel logs are badly scrambled, stacktraces are lost. Printing the timer->function before the BUG_ON() pointed to clocksource_watchdog(). The execution of clocksource_watchdog() can race with a sequence of clocksource_stop_watchdog() .. clocksource_start_watchdog(): expire_timers() detach_timer(timer, true); timer->entry.pprev = NULL; raw_spin_unlock_irq(&base->lock); call_timer_fn clocksource_watchdog() clocksource_watchdog_kthread() or clocksource_unbind() spin_lock_irqsave(&watchdog_lock, flags); clocksource_stop_watchdog(); del_timer(&watchdog_timer); watchdog_running = 0; spin_unlock_irqrestore(&watchdog_lock, flags); spin_lock_irqsave(&watchdog_lock, flags); clocksource_start_watchdog(); add_timer_on(&watchdog_timer, ...); watchdog_running = 1; spin_unlock_irqrestore(&watchdog_lock, flags); spin_lock(&watchdog_lock); add_timer_on(&watchdog_timer, ...); BUG_ON(timer_pending(timer) \|\| !timer->function); timer_pending() -> true BUG() I.e. inside clocksource_watchdog() watchdog_timer could be already armed. Check timer_pending() before calling add_timer_on(). This is sufficient as all operations are synchronized by watchdog_lock. Fixes: `75c5158f70` ("timekeeping: Update clocksource with stop_machine") Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/158048693917.4378.13823603769948933793.stgit@buzz Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2020-02-11 04:34:18 -08:00
arch	x86/apic/msi: Plug non-maskable MSI affinity race	2020-02-11 04:34:18 -08:00
block	block: fix 32 bit overflow in __blkdev_issue_discard()	2020-02-01 09:37:12 +00:00
certs	export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR()	2018-08-22 23:21:44 +09:00
crypto	crypto: api - Fix race condition in crypto_spawn_alg	2020-02-11 04:34:05 -08:00
Documentation	PM / devfreq: Add new name attribute for sysfs	2020-02-05 14:43:34 +00:00
drivers	drm/dp_mst: Remove VCPI while disabling topology mgr	2020-02-11 04:34:16 -08:00
firmware	Fix built-in early-load Intel microcode alignment	2020-01-23 08:21:29 +01:00
fs	cifs: fail i/o on soft mounts if sessionsetup errors out	2020-02-11 04:34:18 -08:00
include	x86/apic/msi: Plug non-maskable MSI affinity race	2020-02-11 04:34:18 -08:00
init	fork: fix some -Wmissing-prototypes warnings	2019-12-05 09:21:04 +01:00
ipc	ipc/msg.c: consolidate all xxxctl_down() functions	2020-02-11 04:33:55 -08:00
kernel	clocksource: Prevent double add_timer_on() for watchdog_timer	2020-02-11 04:34:18 -08:00
lib	lib/test_kasan.c: fix memory leak in kmalloc_oob_krealloc_more()	2020-02-11 04:33:57 -08:00
LICENSES	LICENSES: Remove CC-BY-SA-4.0 license text	2018-10-18 11:28:50 +02:00
mm	mm/page_alloc.c: fix uninitialized memmaps on a partially populated last section	2020-02-11 04:34:18 -08:00
net	net_sched: fix a resource leak in tcindex_set_parms()	2020-02-11 04:34:15 -08:00
samples	samples/bpf: Don't try to remove user's homedir on clean	2020-02-11 04:34:05 -08:00
scripts	scripts/find-unused-docs: Fix massive false positives	2020-02-11 04:34:01 -08:00
security	tomoyo: Use atomic_t for statistics counter	2020-02-05 14:43:38 +00:00
sound	ALSA: hda: Add Clevo W65_67SB the power_save blacklist	2020-02-11 04:33:57 -08:00
tools	tools/kvm_stat: Fix kvm_exit filter name	2020-02-11 04:34:08 -08:00
usr	kbuild: clean compressed initramfs image	2019-10-07 18:57:16 +02:00
virt	KVM: Play nice with read-only memslots when querying host page size	2020-02-11 04:34:17 -08:00
.clang-format	clang-format: Set IndentWrappedFunctionNames false	2018-08-01 18:38:51 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes	.gitattributes: set git diff driver for C source code files	2016-10-07 18:46:30 -07:00
.gitignore	Kbuild updates for v4.17 (2nd)	2018-04-15 17:21:30 -07:00
.mailmap	libnvdimm-for-4.19_misc	2018-08-25 18:13:10 -07:00
COPYING	COPYING: use the new text with points to the license files	2018-03-23 12:41:45 -06:00
CREDITS	9p: remove Ron Minnich from MAINTAINERS	2018-08-17 16:20:26 -07:00
Kbuild	Kbuild updates for v4.15	2017-11-17 17:45:29 -08:00
Kconfig	kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt	2018-08-02 08:06:55 +09:00
MAINTAINERS	USB: rio500: Remove Rio 500 kernel driver	2019-10-17 13:44:47 -07:00
Makefile	Linux 4.19.102	2020-02-05 14:43:55 +00:00
README	Docs: Added a pointer to the formatted docs to README	2018-03-21 09:02:53 -06:00

README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.