linux-kernel - Re: [PATCH] kernel/hung_task.c: Use continuously blocked time when reporting.

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Message-ID: <CACT4Y+aZ17d2R5nauSSHtKBJ0X8QtgPD7ijSv4FRs6G4cg0KjA@mail.gmail.com>
Date:   Tue, 26 Feb 2019 11:01:02 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Ingo Molnar <mingo@...e.hu>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kernel/hung_task.c: Use continuously blocked time when reporting.

On Tue, Feb 26, 2019 at 10:58 AM Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
>
> Since commit a2e514453861dd39 ("kernel/hung_task.c: allow to set checking
> interval separately from timeout") added hung_task_check_interval_secs,
> setting a value different from hung_task_timeout_secs
>
>   echo 0 > /proc/sys/kernel/hung_task_panic
>   echo 120 > /proc/sys/kernel/hung_task_timeout_secs
>   echo 5 > /proc/sys/kernel/hung_task_check_interval_secs
>
> causes confusing output as if the task was blocked for
> hung_task_timeout_secs seconds from the previous report.
>
>   [  399.395930] INFO: task kswapd0:75 blocked for more than 120 seconds.
>   [  405.027637] INFO: task kswapd0:75 blocked for more than 120 seconds.
>   [  410.659725] INFO: task kswapd0:75 blocked for more than 120 seconds.
>   [  416.292860] INFO: task kswapd0:75 blocked for more than 120 seconds.
>   [  421.932305] INFO: task kswapd0:75 blocked for more than 120 seconds.
>
> Although we could update t->last_switch_time after sched_show_task(t) if
> we want to report only every 120 seconds, reporting every 5 seconds might
> not be very bad for monitoring after a problematic situation has started.
> Thus, let's use continuously blocked time instead of updating previously
> reported time.
>
>   [  677.985011] INFO: task kswapd0:80 blocked for more than 122 seconds.
>   [  693.856126] INFO: task kswapd0:80 blocked for more than 138 seconds.
>   [  709.728075] INFO: task kswapd0:80 blocked for more than 154 seconds.
>   [  725.600018] INFO: task kswapd0:80 blocked for more than 170 seconds.
>   [  741.473133] INFO: task kswapd0:80 blocked for more than 186 seconds.
>
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> ---
>  kernel/hung_task.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index 4a91916..6429139 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -126,7 +126,7 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
>                 if (sysctl_hung_task_warnings > 0)
>                         sysctl_hung_task_warnings--;
>                 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
> -                       t->comm, t->pid, timeout);
> +                      t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);

Looks like an improvement to me.

Acked-by: Dmitry Vyukov <dvyukov@...gle.com>



>                 pr_err("      %s %s %.*s\n",
>                         print_tainted(), init_utsname()->release,
>                         (int)strcspn(init_utsname()->version, " "),
> --
> 1.8.3.1