The patch titled
Subject: watchdog: fix barriers when printing backtraces from all CPUs
has been removed from the -mm tree. Its filename was
watchdog-fix-barriers-when-printing-backtraces-from-all-cpus.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Petr Mladek <pmladek@xxxxxxxx>
Subject: watchdog: fix barriers when printing backtraces from all CPUs
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>
---
kernel/watchdog.c | 17 ++++++-----------
1 file changed, 6 insertions(+), 11 deletions(-)
--- a/kernel/watchdog.c~watchdog-fix-barriers-when-printing-backtraces-from-all-cpus
+++ a/kernel/watchdog.c
@@ -410,11 +410,12 @@ static enum hrtimer_restart watchdog_tim
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_tim
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);
_
Patches currently in -mm which might be from pmladek@xxxxxxxx are
