Re: [PATCH v3] drm/msm/dp: fix event thread stuck in wait_event after kthread_stop()

[Dmitry Baryshkov]

On 03/05/2022 19:25, Kuogee Hsieh wrote:
> 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
>
> Changes in v3:
> -- remove unnecessary parenthesis
> -- while(1) to replace while (!kthread_should_stop())
>
> 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>

Let's do it properly:

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>

> ---
>   drivers/gpu/drm/msm/dp/dp_display.c | 13 +++++++++----
>   1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> index c388323..da5c03a 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -1103,15 +1103,20 @@ static int hpd_event_thread(void *data)
>   
>   	dp_priv = (struct dp_display_private *)data;
>   
> -	while (!kthread_should_stop()) {
> +	while (1) {
>   		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) ||
> +					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) ||
> +					kthread_should_stop());
>   		}
> +
> +		if (kthread_should_stop())
> +			break;
> +
>   		spin_lock_irqsave(&dp_priv->event_lock, flag);
>   		todo = &dp_priv->event_list[dp_priv->event_gndx];
>   		if (todo->delay) {


--
With best wishes
Dmitry