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watchdog: fix barriers when printing backtraces from all CPUs 

[ Upstream commit 9f113bf760 ]

Any parallel softlockup reports are skipped when one CPU is already
printing backtraces from all CPUs.

The exclusive rights are synchronized using one bit in
soft_lockup_nmi_warn.  There is also one memory barrier that does not make
much sense.

Use two barriers on the right location to prevent mixing two reports.

[pmladek@suse.com: use bit lock operations to prevent multiple soft-lockup reports]
  Link: https://lkml.kernel.org/r/YFSVsLGVWMXTvlbk@alley

Link: https://lkml.kernel.org/r/20210311122130.6788-6-pmladek@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Laurence Oberman <loberman@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincent Whitchurch <vincent.whitchurch@axis.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
pull/345/head^2
Petr Mladek 2021-04-29 22:54:33 -07:00 committed by Greg Kroah-Hartman
parent a68c246065
commit 5b66867966
1 changed files with 6 additions and 11 deletions
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17
kernel/watchdog.c
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@ -393,11 +393,12 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
if (kvm_check_and_clear_guest_paused())
return HRTIMER_RESTART;
/*
* Prevent multiple soft-lockup reports if one cpu is already
* engaged in dumping all cpu back traces.
*/
if (softlockup_all_cpu_backtrace) {
/* Prevent multiple soft-lockup reports if one cpu is already
* engaged in dumping cpu back traces
*/
if (test_and_set_bit(0, &soft_lockup_nmi_warn))
if (test_and_set_bit_lock(0, &soft_lockup_nmi_warn))
return HRTIMER_RESTART;
}
@ -415,14 +416,8 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
dump_stack();
if (softlockup_all_cpu_backtrace) {
/* Avoid generating two back traces for current
* given that one is already made above
*/
trigger_allbutself_cpu_backtrace();
clear_bit(0, &soft_lockup_nmi_warn);
/* Barrier to sync with other cpus */
smp_mb__after_atomic();
clear_bit_unlock(0, &soft_lockup_nmi_warn);
}
add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);