linux-kernel - Re: [PATCH v2] drm/msm/dp: fix event thread stuck in wait_event after kthread

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Date:   Mon, 2 May 2022 18:13:29 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>, agross@...nel.org,
        airlied@...ux.ie, bjorn.andersson@...aro.org, daniel@...ll.ch,
        dianders@...omium.org, dmitry.baryshkov@...aro.org,
        robdclark@...il.com, sean@...rly.run, vkoul@...nel.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 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@...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) ||

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.