linux-kernel - [PATCH v1] drm/scheduler: Fix lockup in drm_sched_entity

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Message-Id: <20221123001303.533968-1-dmitry.osipenko@collabora.com>
Date:   Wed, 23 Nov 2022 03:13:03 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Luben Tuikov <luben.tuikov@....com>,
        Christian König <christian.koenig@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH v1] drm/scheduler: Fix lockup in drm_sched_entity_kill()

The drm_sched_entity_kill() is invoked twice by drm_sched_entity_destroy()
while userspace process is exiting or being killed. First time it's invoked
when sched entity is flushed and second time when entity is released. This
causes a lockup within wait_for_completion(entity_idle) due to how completion
API works.

Calling wait_for_completion() more times than complete() was invoked is a
error condition that causes lockup because completion internally uses
counter for complete/wait calls. The complete_all() must be used instead
in such cases.

This patch fixes lockup of Panfrost driver that is reproducible by killing
any application in a middle of 3d drawing operation.

Fixes: 2fdb8a8f07c2 ("drm/scheduler: rework entity flush, kill and fini")
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
---
 drivers/gpu/drm/scheduler/sched_entity.c | 2 +-
 drivers/gpu/drm/scheduler/sched_main.c   | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
index fe09e5be79bd..15d04a0ec623 100644
--- a/drivers/gpu/drm/scheduler/sched_entity.c
+++ b/drivers/gpu/drm/scheduler/sched_entity.c
@@ -81,7 +81,7 @@ int drm_sched_entity_init(struct drm_sched_entity *entity,
 	init_completion(&entity->entity_idle);
 
 	/* We start in an idle state. */
-	complete(&entity->entity_idle);
+	complete_all(&entity->entity_idle);
 
 	spin_lock_init(&entity->rq_lock);
 	spsc_queue_init(&entity->job_queue);
diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
index 6ce04c2e90c0..857ec20be9e8 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -1026,7 +1026,7 @@ static int drm_sched_main(void *param)
 		sched_job = drm_sched_entity_pop_job(entity);
 
 		if (!sched_job) {
-			complete(&entity->entity_idle);
+			complete_all(&entity->entity_idle);
 			continue;
 		}
 
@@ -1037,7 +1037,7 @@ static int drm_sched_main(void *param)
 
 		trace_drm_run_job(sched_job, entity);
 		fence = sched->ops->run_job(sched_job);
-		complete(&entity->entity_idle);
+		complete_all(&entity->entity_idle);
 		drm_sched_fence_scheduled(s_fence);
 
 		if (!IS_ERR_OR_NULL(fence)) {
-- 
2.38.1