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84a8404988
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Waiman Long 84a8404988 driver/dma/ioat: Call del_timer_sync() without holding prep_lock 
[ Upstream commit cfb03be6c7 ]

The following lockdep splat was observed:

[ 1222.241750] ======================================================
[ 1222.271301] WARNING: possible circular locking dependency detected
[ 1222.301060] 4.16.0-10.el8+5.x86_64+debug #1 Not tainted
[ 1222.326659] ------------------------------------------------------
[ 1222.356565] systemd-shutdow/1 is trying to acquire lock:
[ 1222.382660]  ((&ioat_chan->timer)){+.-.}, at: [<00000000f71e1a28>] del_timer_sync+0x5/0xf0
[ 1222.422928]
[ 1222.422928] but task is already holding lock:
[ 1222.451743]  (&(&ioat_chan->prep_lock)->rlock){+.-.}, at: [<000000008ea98b12>] ioat_shutdown+0x86/0x100 [ioatdma]
   :
[ 1223.524987] Chain exists of:
[ 1223.524987]   (&ioat_chan->timer) --> &(&ioat_chan->cleanup_lock)->rlock --> &(&ioat_chan->prep_lock)->rlock
[ 1223.524987]
[ 1223.594082]  Possible unsafe locking scenario:
[ 1223.594082]
[ 1223.622630]        CPU0                    CPU1
[ 1223.645080]        ----                    ----
[ 1223.667404]   lock(&(&ioat_chan->prep_lock)->rlock);
[ 1223.691535]                                lock(&(&ioat_chan->cleanup_lock)->rlock);
[ 1223.728657]                                lock(&(&ioat_chan->prep_lock)->rlock);
[ 1223.765122]   lock((&ioat_chan->timer));
[ 1223.784095]
[ 1223.784095]  *** DEADLOCK ***
[ 1223.784095]
[ 1223.813492] 4 locks held by systemd-shutdow/1:
[ 1223.834677]  #0:  (reboot_mutex){+.+.}, at: [<0000000056d33456>] SYSC_reboot+0x10f/0x300
[ 1223.873310]  #1:  (&dev->mutex){....}, at: [<00000000258dfdd7>] device_shutdown+0x1c8/0x660
[ 1223.913604]  #2:  (&dev->mutex){....}, at: [<0000000068331147>] device_shutdown+0x1d6/0x660
[ 1223.954000]  #3:  (&(&ioat_chan->prep_lock)->rlock){+.-.}, at: [<000000008ea98b12>] ioat_shutdown+0x86/0x100 [ioatdma]

In the ioat_shutdown() function:

	spin_lock_bh(&ioat_chan->prep_lock);
	set_bit(IOAT_CHAN_DOWN, &ioat_chan->state);
	del_timer_sync(&ioat_chan->timer);
	spin_unlock_bh(&ioat_chan->prep_lock);

According to the synchronization rule for the del_timer_sync() function,
the caller must not hold locks which would prevent completion of the
timer's handler.

The timer structure has its own lock that manages its synchronization.
Setting the IOAT_CHAN_DOWN bit should prevent other CPUs from
trying to use that device anyway, there is probably no need to call
del_timer_sync() while holding the prep_lock. So the del_timer_sync()
call is now moved outside of the prep_lock critical section to prevent
the circular lock dependency.

Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2018-11-13 11:08:36 -08:00
arch KVM: nVMX: Clear reserved bits of #DB exit qualification 2018-11-13 11:08:32 -08:00
block block, bfq: correctly charge and reset entity service in all cases 2018-11-13 11:08:28 -08:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto Revert "net: simplify sock_poll_wait" 2018-11-04 14:50:51 +01:00
Documentation Code of Conduct: Change the contact email address 2018-10-22 07:33:36 +01:00
drivers driver/dma/ioat: Call del_timer_sync() without holding prep_lock 2018-11-13 11:08:36 -08:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs f2fs: fix to recover inode's i_flags during POR 2018-11-13 11:08:36 -08:00
include UAPI: ndctl: Fix g++-unsupported initialisation in headers 2018-11-13 11:08:32 -08:00
init Kbuild updates for v4.19 (2nd) 2018-08-25 13:40:38 -07:00
ipc ipc/shm.c: use ERR_CAST() for shm_lock() error return 2018-10-05 16:32:04 -07:00
kernel bpf/verifier: fix verifier instability 2018-11-13 11:08:28 -08:00
lib locking/lockdep: Fix debug_locks off performance problem 2018-11-13 11:08:20 -08:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
mm mremap: properly flush TLB before releasing the page 2018-10-18 11:30:52 +02:00
net xprtrdma: Reset credit grant properly after a disconnect 2018-11-13 11:08:34 -08:00
samples samples: disable CONFIG_SAMPLES for UML 2018-10-11 02:15:46 +09:00
scripts Kbuild fixes for v4.19 (2nd) 2018-10-11 19:23:07 +02:00
security Smack: ptrace capability use fixes 2018-11-13 11:08:36 -08:00
sound ALSA: hda - Fix incorrect clearance of thinkpad_acpi hooks 2018-11-13 11:08:19 -08:00
tools perf tests: Fix record+probe_libc_inet_pton.sh without ping's debuginfo 2018-11-13 11:08:28 -08:00
usr initramfs: move gen_initramfs_list.sh from scripts/ to usr/ 2018-08-22 23:21:44 +09:00
virt KVM: Remove obsolete kvm_unmap_hva notifier backend 2018-09-07 15:06:02 +02:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.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 MAINTAINERS: Add an entry for the code of conduct 2018-10-22 07:33:36 +01:00
Makefile Linux 4.19.1 2018-11-04 14:50:54 +01:00
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.