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SubjectRe: [PATCH v2] drm/msm/dp: fix event thread stuck in wait_event after kthread_stop()
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@linaro.org>
> Fixes: 570d3e5d28db ("drm/msm/dp: stop event kernel thread when DP unbind")
> Signed-off-by: Kuogee Hsieh <quic_khsieh@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.

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