From: Petr Mladek <pmladek@suse.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>
Cc: Laurence Oberman <loberman@redhat.com>,
Vincent Whitchurch <vincent.whitchurch@axis.com>,
Michal Hocko <mhocko@suse.com>,
linux-kernel@vger.kernel.org, Petr Mladek <pmladek@suse.com>
Subject: [PATCH v2 5/7] watchdog: Fix barriers when printing backtraces from all CPUs
Date: Thu, 10 Dec 2020 17:00:36 +0100 [thread overview]
Message-ID: <20201210160038.31441-6-pmladek@suse.com> (raw)
In-Reply-To: <20201210160038.31441-1-pmladek@suse.com>
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.
Signed-off-by: Petr Mladek <pmladek@suse.com>
---
kernel/watchdog.c | 24 +++++++++++++++---------
1 file changed, 15 insertions(+), 9 deletions(-)
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index dc8a0bf943f5..6dc1f79e36aa 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -409,12 +409,18 @@ 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))
return HRTIMER_RESTART;
+ /*
+ * Make sure that reports are serialized. Start
+ * printing after getting the exclusive rights.
+ */
+ smp_mb__after_atomic();
}
/* Start period for the next softlockup warning. */
@@ -431,14 +437,14 @@ 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();
-
+ /*
+ * Make sure that everything is printed before
+ * another CPU is allowed to report lockup again.
+ */
+ smp_mb__before_atomic();
+ /* Allow a further report. */
clear_bit(0, &soft_lockup_nmi_warn);
- /* Barrier to sync with other cpus */
- smp_mb__after_atomic();
}
add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
--
2.26.2
next prev parent reply other threads:[~2020-12-10 16:02 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-10 16:00 [PATCH v2 0/7] watchdog/softlockup: Report overall time and some cleanup Petr Mladek
2020-12-10 16:00 ` [PATCH v2 1/7] watchdog: Rename __touch_watchdog() to a better descriptive name Petr Mladek
2020-12-10 16:00 ` [PATCH v2 2/7] watchdog: Explicitly update timestamp when reporting softlockup Petr Mladek
2020-12-10 16:00 ` [PATCH v2 3/7] watchdog/softlockup: Report the overall time of softlockups Petr Mladek
2020-12-10 16:00 ` [PATCH v2 4/7] watchdog/softlockup: Remove logic that tried to prevent repeated reports Petr Mladek
2020-12-10 16:00 ` Petr Mladek [this message]
2020-12-10 16:00 ` [PATCH v2 6/7] watchdog: Cleanup handling of false positives Petr Mladek
2020-12-10 16:00 ` [PATCH v2 7/7] Test softlockup Petr Mladek
2021-01-03 15:03 ` 3cc3ef45b2: RIP:version_proc_show kernel test robot
2021-01-05 9:37 ` Petr Mladek
2021-03-11 12:21 [PATCH v2 0/7] watchdog/softlockup: Report overall time and some cleanup Petr Mladek
2021-03-11 12:21 ` [PATCH v2 5/7] watchdog: Fix barriers when printing backtraces from all CPUs Petr Mladek
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