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    SubjectRe: [PATCH RFC] kernel/hung_task.c: disable on suspend
    On 09/13, Rafael J. Wysocki wrote:
    >
    > On Wed, Sep 12, 2018 at 6:11 PM Vitaly Kuznetsov <vkuznets@redhat.com> 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
    >
    > This actually is a good catch, but the problem is related to what
    > happens to the monotonic clock during suspend to idle.
    >
    > The clock issue needs to be addressed anyway IMO and then this problem
    > will go away automatically.

    I don't understand your discussion with Vitaly, but shouldn't we make
    khungtaskd thread freezable anyway?

    Oleg.

    --- x/kernel/hung_task.c
    +++ x/kernel/hung_task.c
    @@ -185,7 +185,7 @@ static void check_hung_uninterruptible_t
    hung_task_show_lock = false;
    rcu_read_lock();
    for_each_process_thread(g, t) {
    - if (!max_count--)
    + if (!max_count-- || freezing(current))
    goto unlock;
    if (!--batch_count) {
    batch_count = HUNG_TASK_BATCHING;
    @@ -249,6 +249,7 @@ static int watchdog(void *dummy)
    {
    unsigned long hung_last_checked = jiffies;

    + set_freezable();
    set_user_nice(current, 0);

    for ( ; ; ) {
    @@ -266,7 +267,7 @@ static int watchdog(void *dummy)
    hung_last_checked = jiffies;
    continue;
    }
    - schedule_timeout_interruptible(t);
    + freezable_schedule_timeout_interruptible(t);
    }

    return 0;
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