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SubjectRe: [PATCH] kernel/hung_task.c: disable on suspend
Date
On Thursday, September 13, 2018 6:08:51 PM CEST Vitaly Kuznetsov wrote:
> It is possible to observe hung_task complaints when system goes to
> suspend-to-idle 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@redhat.com>
> ---
> Changes since RFC:
> - Add PM_HIBERNATION_PREPARE/PM_POST_HIBERNATION for consistency
> [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:
> + hung_detector_suspended = true;
> + break;
> + case PM_POST_SUSPEND:
> + case PM_POST_HIBERNATION:
> + 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);

Since you are adding the notifier anyway, what about designing it to make
the thread wait on _PREPARE until the notifier kicks it again on exit
fron suspend/hibernation?

> 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;
>

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