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watchdog: update saved interrupts during check

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Currently, arch_touch_nmi_watchdog() causes an early return that skips
updating hrtimer_interrupts_saved.  This leads to stale comparisons and
delayed lockup detection.

I found this issue because in our system the serial console is fairly
chatty.  For example, the 8250 console driver frequently calls
touch_nmi_watchdog() via console_write().  If a CPU locks up after a timer
interrupt but before next watchdog check, we see the following sequence:

  * watchdog_hardlockup_check() saves counter (e.g., 1000)
  * Timer runs and updates the counter (1001)
  * touch_nmi_watchdog() is called
  * CPU locks up
  * 10s pass: check() notices touch, returns early, skips update
  * 10s pass: check() saves counter (1001)
  * 10s pass: check() finally detects lockup

This delays detection to 30 seconds.  With this fix, we detect the lockup
in 20 seconds.

Link: https://lkml.kernel.org/r/20260312-hardlockup-watchdog-fixes-v2-2-45bd8a0cc7ed@google.com
Signed-off-by: Mayank Rungta <mrungta@google.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Li Huafei <lihuafei1@huawei.com>
Cc: Max Kellermann <max.kellermann@ionos.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Stephane Erainan <eranian@google.com>
Cc: Wang Jinchao <wangjinchao600@gmail.com>
Cc: Yunhui Cui <cuiyunhui@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Mayank Rungta
2026-03-12 16:22:03 -07:00
committed by Andrew Morton
parent 3e811cae32
commit 746bb7fa91
1 changed files with 13 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

18
kernel/watchdog.c
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@@ -159,21 +159,28 @@ void watchdog_hardlockup_touch_cpu(unsigned int cpu)
per_cpu(watchdog_hardlockup_touched, cpu) = true;
}
static bool is_hardlockup(unsigned int cpu)
static void watchdog_hardlockup_update(unsigned int cpu)
{
int hrint = atomic_read(&per_cpu(hrtimer_interrupts, cpu));
if (per_cpu(hrtimer_interrupts_saved, cpu) == hrint)
return true;
/*
* NOTE: we don't need any fancy atomic_t or READ_ONCE/WRITE_ONCE
* for hrtimer_interrupts_saved. hrtimer_interrupts_saved is
* written/read by a single CPU.
*/
per_cpu(hrtimer_interrupts_saved, cpu) = hrint;
}
return false;
static bool is_hardlockup(unsigned int cpu)
{
int hrint = atomic_read(&per_cpu(hrtimer_interrupts, cpu));
if (per_cpu(hrtimer_interrupts_saved, cpu) != hrint) {
watchdog_hardlockup_update(cpu);
return false;
}
return true;
}
static void watchdog_hardlockup_kick(void)
@@ -191,6 +198,7 @@ void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs)
unsigned long flags;
if (per_cpu(watchdog_hardlockup_touched, cpu)) {
watchdog_hardlockup_update(cpu);
per_cpu(watchdog_hardlockup_touched, cpu) = false;
return;
}