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

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Message-ID: <0cd21ffb-448f-3dcf-df29-959da50c9108@quicinc.com>
Date:   Mon, 2 May 2022 14:53:01 -0700
From:   Abhinav Kumar <quic_abhinavk@...cinc.com>
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>, <dmitry.baryshkov@...aro.org>,
        <bjorn.andersson@...aro.org>
CC:     <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] drm/msm/dp: fix event thread stuck in wait_event after
 kthread_sop()



On 5/2/2022 2:50 PM, 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().
> 
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>
> ---
>   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) ||
> +					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) {