Re: [PATCH v2 2/5] watchdog: Update saved interrupts during check

[Petr Mladek <pmladek@suse.com>]

On Thu 2026-03-12 16:22:03, Mayank Rungta via B4 Relay wrote:
> From: Mayank Rungta <mrungta@google.com>
> 
> 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.
> 
> Reviewed-by: Douglas Anderson <dianders@chromium.org>
> Signed-off-by: Mayank Rungta <mrungta@google.com>

I agree with Doug's analyze and it looks good to me:

Reviewed-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr