From: Petr Mladek pmladek@suse.com
[ 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@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 --- kernel/watchdog.c | 17 ++++++----------- 1 file changed, 6 insertions(+), 11 deletions(-)
diff --git a/kernel/watchdog.c b/kernel/watchdog.c index b8d4182d14cc..8cf0678378d2 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -410,11 +410,12 @@ 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; }
@@ -432,14 +433,8 @@ 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);