Re: [PATCH v2] drm/msm/dp: fix event thread stuck in wait_event after kthread_stop()

[Kuogee Hsieh]

On 5/2/2022 6:13 PM, Stephen Boyd wrote:
> Quoting Kuogee Hsieh (2022-05-02 16:04:28)
> > Event thread supposed to exit from its while loop after kthread_stop().
> > However there may has possibility that event thread is pending in the
> > middle of wait_event due to condition checking never become true.
> > To make sure event thread exit its loop after kthread_stop(), this
> > patch OR kthread_should_stop() into wait_event's condition checking
> > so that event thread will exit its loop after kernal_stop().
> >
> > Changes in v2:
> > --  correct spelling error at commit title
> >
> > Reported-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
> > Fixes: 570d3e5d28db ("drm/msm/dp: stop event kernel thread when DP unbind")
> > Signed-off-by: Kuogee Hsieh <quic_khsieh@xxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/msm/dp/dp_display.c | 11 ++++++++---
> >   1 file changed, 8 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> > index c388323..5200a58 100644
> > --- a/drivers/gpu/drm/msm/dp/dp_display.c
> > +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> > @@ -1106,12 +1106,17 @@ static int hpd_event_thread(void *data)
> >          while (!kthread_should_stop()) {
> >                  if (timeout_mode) {
> >                          wait_event_timeout(dp_priv->event_q,
> > -                               (dp_priv->event_pndx == dp_priv->event_gndx),
> > -                                               EVENT_TIMEOUT);
> > +                               ((dp_priv->event_pndx == dp_priv->event_gndx) ||
> Why the parenthesis (before and after)?
>
> > +                                       kthread_should_stop()), EVENT_TIMEOUT);
> >                  } else {
> >                          wait_event_interruptible(dp_priv->event_q,
> > -                               (dp_priv->event_pndx != dp_priv->event_gndx));
> > +                               ((dp_priv->event_pndx != dp_priv->event_gndx) ||
> Why the parenthesis (before and after)?
>
> > +                                       kthread_should_stop()));
> >                  }
> > +
> > +               if(kthread_should_stop())
> Missing space after if
>
> > +                       break;
> Is it possible to move the wait_event to the end of the loop and always
> run the loop initially? That way we don't have to check for
> kthread_should_stop() again.

no, since we have to make sure q is not empty so that we can proceed to 
service events.

bu ti thin we can use while (1) instead of while 
(!kthread_should_stop()) since we have add kthread_should_stop() into 
wait_event condition checking.