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

[Stephen Boyd]

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 at linaro.org>
> Fixes: 570d3e5d28db ("drm/msm/dp: stop event kernel thread when DP unbind")
> Signed-off-by: Kuogee Hsieh <quic_khsieh at quicinc.com>
> ---
>  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.