[PATCH] power: suspend: Add suspend timeout handler

[<josephjang@google.com>]

Thank you Petr for promptly reply.

> On Fri 2020-10-16 11:51:09, Joseph Jang wrote:
> > From: josephjang <josephjang@google.com>
> >
> > Add suspend timeout handler to prevent device stuck during suspend/
> > resume process. Suspend timeout handler will dump disk sleep task
> > at first round timeout and trigger kernel panic at second round timeout.
> > The default timer for each round is 30 seconds.

> A better solution would be to resume instead of panic().


[Joseph] suspend_timeout() will trigger kernel panic() only when
suspend thread stuck (deadlock/hang) for 2*30 seconds.
At that moment, I don't know how to resume the suspend thread. So I
just could trigger panic to reboot system.
If you have better suggestions, I am willing to study it.

> > Note: Can use following command to simulate suspend hang for testing.
> >     adb shell echo 1 > /sys/power/pm_hang

> This looks dangerous. It adds a simple way to panic() the system.

> First, it should get enabled separately. e.g.
> CONFIG_TEST_PM_SLEEP_MONITOR.

> Second, I would add it as a module that might get loaded
> and unloaded.


[Joseph] Agree to enable new compile flag for test module.
I think it is better to create separate patch for the new test module right?

> > diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
> > index 8b1bb5ee7e5d..6f2679cfd9d1 100644
> > --- a/kernel/power/suspend.c
> > +++ b/kernel/power/suspend.c
> Using kthread looks like an overkill to me. I wonder how this actually
> works when the kthreads get freezed. It might be enough to implement
> just a timer callback. Start the timer in start_suspend_mon() and
> delete it in stop_suspend_mon(). Or do I miss anything?

> Anyway, the kthread implementation looks a but hairy. If you really
> need to use kthread, I suggest to use kthread_worker API. You would
> need to run an init work to setup the RT scheduling. Then you
> could just call kthread_queue_delayed_work(()
> and kthread_cancel_delayed_work_sync() to start and stop
> the monitor.



[Joseph]
Actually, I had ever think we just need to use
add_timer()/del_timer_sync() for start_suspend_mon()/stop_suspend_mon()  
before.

But I am not sure if add_timer() may cause any performance impact in
suspend thread or not.
So I try to create a suspend monitor kthread and just flip the flag in
suspend thread.


> > @@ -114,6 +251,10 @@ static void s2idle_enter(void)
> >       s2idle_state = S2IDLE_STATE_NONE;
> >       raw_spin_unlock_irq(&s2idle_lock);
> >
> > +#ifdef CONFIG_PM_SLEEP_MONITOR
> > +     start_suspend_mon();
> > +#endif

> It is better to solve this by defining start_suspend_mon() as empty
> function when the config option is disabled. For example, see
> how  vgacon_text_force() is defined in console.h.


[Joseph] Thank you for good suggestions.
May I know if I could use IS_ENABLED() ?
if (IS_ENABLED(CONFIG_PM_SLEEP_MONITOR))
     start_suspend_mon();

> Best Regards,
> Petr