linux-kernel - Re: [PATCH v3] kernel/hung

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Date:   Wed, 17 Oct 2018 09:32:48 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH v3] kernel/hung_task.c: disable on suspend

On Tue, Oct 16, 2018 at 6:55 PM Vitaly Kuznetsov <vkuznets@...hat.com> wrote:
>
> It is possible to observe hung_task complaints when system goes to
> suspend-to-idle state:
>
>  # echo freeze > /sys/power/state
>
>  PM: Syncing filesystems ... done.
>  Freezing user space processes ... (elapsed 0.001 seconds) done.
>  OOM killer disabled.
>  Freezing remaining freezable tasks ... (elapsed 0.002 seconds) done.
>  sd 0:0:0:0: [sda] Synchronizing SCSI cache
>  INFO: task bash:1569 blocked for more than 120 seconds.
>        Not tainted 4.19.0-rc3_+ #687
>  "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>  bash            D    0  1569    604 0x00000000
>  Call Trace:
>   ? __schedule+0x1fe/0x7e0
>   schedule+0x28/0x80
>   suspend_devices_and_enter+0x4ac/0x750
>   pm_suspend+0x2c0/0x310
>
> Register a PM notifier to disable the detector on suspend and re-enable
> back on wakeup.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
> Changes since v2:
> - Resurrect 'v1' as zeroing timeouts can be racy [Rafael J. Wysocki]
> ---
>  kernel/hung_task.c | 28 +++++++++++++++++++++++++++-
>  1 file changed, 27 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index b9132d1269ef..41955c5d8427 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -15,6 +15,7 @@
>  #include <linux/lockdep.h>
>  #include <linux/export.h>
>  #include <linux/sysctl.h>
> +#include <linux/suspend.h>
>  #include <linux/utsname.h>
>  #include <linux/sched/signal.h>
>  #include <linux/sched/debug.h>
> @@ -242,6 +243,26 @@ void reset_hung_task_detector(void)
>  }
>  EXPORT_SYMBOL_GPL(reset_hung_task_detector);
>
> +static bool hung_detector_suspended;
> +
> +static int hungtask_pm_notify(struct notifier_block *self,
> +                             unsigned long action, void *hcpu)
> +{
> +       switch (action) {
> +       case PM_SUSPEND_PREPARE:
> +       case PM_HIBERNATION_PREPARE:

Please add PM_RESTORE_PREPARE here ->

> +               hung_detector_suspended = true;
> +               break;
> +       case PM_POST_SUSPEND:
> +       case PM_POST_HIBERNATION:

-> and PM_POST_RESTORE here for completeness.

> +               hung_detector_suspended = false;
> +               break;
> +       default:
> +               break;
> +       }
> +       return NOTIFY_OK;
> +}
> +
>  /*
>   * kthread which checks for tasks stuck in D state
>   */
> @@ -261,7 +282,8 @@ static int watchdog(void *dummy)
>                 interval = min_t(unsigned long, interval, timeout);
>                 t = hung_timeout_jiffies(hung_last_checked, interval);
>                 if (t <= 0) {
> -                       if (!atomic_xchg(&reset_hung_task, 0))
> +                       if (!atomic_xchg(&reset_hung_task, 0) &&
> +                           !hung_detector_suspended)
>                                 check_hung_uninterruptible_tasks(timeout);
>                         hung_last_checked = jiffies;
>                         continue;
> @@ -275,6 +297,10 @@ static int watchdog(void *dummy)
>  static int __init hung_task_init(void)
>  {
>         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
> +
> +       /* Disable hung task detector on suspend */
> +       pm_notifier(hungtask_pm_notify, 0);
> +
>         watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
>
>         return 0;
> --

Apart from the above it is fine by me.

This is the minimum fix for the issue at hand AFAICS.

Thanks,
Rafael