From: Petr Mladek <pmladek@xxxxxxxx> [ Upstream commit 9f113bf760ca90d709f8f89a733d10abb1f04a83 ] 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@xxxxxxxx: 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@xxxxxxxx Signed-off-by: Petr Mladek <pmladek@xxxxxxxx> Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Laurence Oberman <loberman@xxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- kernel/watchdog.c | 17 ++++++----------- 1 file changed, 6 insertions(+), 11 deletions(-) diff --git a/kernel/watchdog.c b/kernel/watchdog.c index 122e272ad7f2..01bf977090dc 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -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); -- 2.30.2
