linux-kernel - [PATCH 5.10 191/452] drm/msm/dp: fix event thread stuck in wait_event after kthread

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Date:   Tue,  7 Jun 2022 19:00:48 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.10 191/452] drm/msm/dp: fix event thread stuck in wait_event after kthread_stop()

From: Kuogee Hsieh <quic_khsieh@...cinc.com>

[ Upstream commit 2f9b5b3ae2eb625b75a898212a76f3b8c6d0d2b0 ]

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>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Reviewed-by: Stephen Boyd <swboyd@...omium.org>
Patchwork: https://patchwork.freedesktop.org/patch/484576/
Link: https://lore.kernel.org/r/1651595136-24312-1-git-send-email-quic_khsieh@quicinc.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Signed-off-by: Sasha Levin <sashal@...nel.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 09c8e50da68d..ebd05678a27b 100644
--- a/drivers/gpu/drm/msm/dp/dp_display.c
+++ b/drivers/gpu/drm/msm/dp/dp_display.c
@@ -998,15 +998,20 @@ 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) {
-- 
2.35.1