linux-kernel - Re: [PATCH v3] drm/msm/dp: fix event thread stuck in wait_event after kthread

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Message-ID: <834eeda0-12b0-3f16-8ca2-89175c1de186@linaro.org>
Date:   Wed, 4 May 2022 21:38:05 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>, robdclark@...il.com,
        sean@...rly.run, swboyd@...omium.org, dianders@...omium.org,
        vkoul@...nel.org, daniel@...ll.ch, airlied@...ux.ie,
        agross@...nel.org, bjorn.andersson@...aro.org
Cc:     quic_abhinavk@...cinc.com, quic_aravindh@...cinc.com,
        quic_sbillaka@...cinc.com, freedreno@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] drm/msm/dp: fix event thread stuck in wait_event after
 kthread_stop()

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

Let's do it properly:

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

> ---
>   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