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

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Message-ID: <1651595136-24312-1-git-send-email-quic_khsieh@quicinc.com>
Date:   Tue, 3 May 2022 09:25:36 -0700
From:   Kuogee Hsieh <quic_khsieh@...cinc.com>
To:     <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_abhinavk@...cinc.com>, <quic_aravindh@...cinc.com>,
        <quic_khsieh@...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: [PATCH v3] drm/msm/dp: fix event thread stuck in wait_event after kthread_stop()

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>
---
 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) {
-- 
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a Linux Foundation Collaborative Project