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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        =?UTF-8?q?Christian=20K=C3=B6nig?= <christian.koenig@amd.com>,
        Andrey Grodzovsky <andrey.grodzovsky@amd.com>,
        Monk.liu@amd.com, Alex Deucher <alexander.deucher@amd.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.2 038/143] drm/scheduler: use job count instead of peek
Date:   Wed,  4 Sep 2019 19:53:01 +0200
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[ Upstream commit e1b4ce25dbc93ab0cb8ed0f236a3b9ff7b03802c ]

The spsc_queue_peek function is accessing queue->head which belongs to
the consumer thread and shouldn't be accessed by the producer

This is fixing a rare race condition when destroying entities.

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Monk.liu@amd.com
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/gpu/drm/scheduler/sched_entity.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
index 35ddbec1375ae..671c90f34ede6 100644
--- a/drivers/gpu/drm/scheduler/sched_entity.c
+++ b/drivers/gpu/drm/scheduler/sched_entity.c
@@ -95,7 +95,7 @@ static bool drm_sched_entity_is_idle(struct drm_sched_entity *entity)
 	rmb(); /* for list_empty to work without lock */
 
 	if (list_empty(&entity->list) ||
-	    spsc_queue_peek(&entity->job_queue) == NULL)
+	    spsc_queue_count(&entity->job_queue) == 0)
 		return true;
 
 	return false;
@@ -281,7 +281,7 @@ void drm_sched_entity_fini(struct drm_sched_entity *entity)
 	/* Consumption of existing IBs wasn't completed. Forcefully
 	 * remove them here.
 	 */
-	if (spsc_queue_peek(&entity->job_queue)) {
+	if (spsc_queue_count(&entity->job_queue)) {
 		if (sched) {
 			/* Park the kernel for a moment to make sure it isn't processing
 			 * our enity.
-- 
2.20.1