The patch titled
Subject: watchdog/softlockup: use printk_cpu_sync_get_irqsave() to serialize reporting
has been added to the -mm mm-nonmm-unstable branch. Its filename is
watchdog-softlockup-use-printk_cpu_sync_get_irqsave-to-serialize-reporting.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/watchdog-softlockup-use-printk_cpu_sync_get_irqsave-to-serialize-reporting.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Douglas Anderson <dianders@xxxxxxxxxxxx>
Subject: watchdog/softlockup: use printk_cpu_sync_get_irqsave() to serialize reporting
Date: Wed, 20 Dec 2023 13:15:35 -0800
Instead of introducing a spinlock, use printk_cpu_sync_get_irqsave() and
printk_cpu_sync_put_irqrestore() to serialize softlockup reporting. Alone
this doesn't have any real advantage over the spinlock, but this will
allow us to use the same function in a future change to also serialize
hardlockup crawls.
NOTE: for the most part this serialization is important because we often
end up in the show_regs() path and that has no built-in serialization if
there are multiple callers at once. However, even in the case where we
end up in the dump_stack() path this still has some advantages because the
stack will be guaranteed to be together in the logs with the lockup
message with no interleaving.
NOTE: the fact that printk_cpu_sync_get_irqsave() is allowed to be called
multiple times on the same CPU is important here. Specifically we hold
the "lock" while calling dump_stack() which also gets the same "lock".
This is explicitly documented to be OK and means we don't need to
introduce a variant of dump_stack() that doesn't grab the lock.
Link: https://lkml.kernel.org/r/20231220131534.2.Ia5906525d440d8e8383cde31b7c61c2aadc8f907@changeid
Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
Cc: John Ogness <john.ogness@xxxxxxxxxxxxx>
Cc: Lecopzer Chen <lecopzer.chen@xxxxxxxxxxxx>
Cc: Li Zhe <lizhe.67@xxxxxxxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
Cc: Pingfan Liu <kernelfans@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/watchdog.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
--- a/kernel/watchdog.c~watchdog-softlockup-use-printk_cpu_sync_get_irqsave-to-serialize-reporting
+++ a/kernel/watchdog.c
@@ -454,7 +454,7 @@ static enum hrtimer_restart watchdog_tim
struct pt_regs *regs = get_irq_regs();
int duration;
int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
- static DEFINE_SPINLOCK(watchdog_output_lock);
+ unsigned long flags;
if (!watchdog_enabled)
return HRTIMER_NORESTART;
@@ -521,7 +521,7 @@ static enum hrtimer_restart watchdog_tim
/* Start period for the next softlockup warning. */
update_report_ts();
- spin_lock(&watchdog_output_lock);
+ printk_cpu_sync_get_irqsave(flags);
pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
smp_processor_id(), duration,
current->comm, task_pid_nr(current));
@@ -531,7 +531,7 @@ static enum hrtimer_restart watchdog_tim
show_regs(regs);
else
dump_stack();
- spin_unlock(&watchdog_output_lock);
+ printk_cpu_sync_put_irqrestore(flags);
if (softlockup_all_cpu_backtrace) {
trigger_allbutcpu_cpu_backtrace(smp_processor_id());
_
Patches currently in -mm which might be from dianders@xxxxxxxxxxxx are
watchdog-hardlockup-adopt-softlockup-logic-avoiding-double-dumps.patch
watchdog-softlockup-use-printk_cpu_sync_get_irqsave-to-serialize-reporting.patch
watchdog-hardlockup-use-printk_cpu_sync_get_irqsave-to-serialize-reporting.patch
watchdog-if-panicking-and-we-dumped-everything-dont-re-enable-dumping.patch
