[PATCH v1] drm/sched: fix deadlock in drm_sched_entity_kill_jobs_cb

[Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>]

https://gitlab.freedesktop.org/mesa/mesa/-/issues/13908 pointed out
a possible deadlock:

[ 1231.611031]  Possible interrupt unsafe locking scenario:

[ 1231.611033]        CPU0                    CPU1
[ 1231.611034]        ----                    ----
[ 1231.611035]   lock(&xa->xa_lock#17);
[ 1231.611038]                                local_irq_disable();
[ 1231.611039]                                lock(&fence->lock);
[ 1231.611041]                                lock(&xa->xa_lock#17);
[ 1231.611044]   <Interrupt>
[ 1231.611045]     lock(&fence->lock);
[ 1231.611047]
                *** DEADLOCK ***

My initial fix was to replace xa_erase by xa_erase_irq, but Christian
pointed out that calling dma_fence_add_callback from a callback can
also deadlock if the signalling fence and the one passed to
dma_fence_add_callback share the same lock.

To fix both issues, the code iterating on dependencies and re-arming them
is moved out to drm_sched_entity_kill_jobs_work.

Suggested-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
---
 drivers/gpu/drm/scheduler/sched_entity.c | 34 +++++++++++++-----------
 1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
index c8e949f4a568..fe174a4857be 100644
--- a/drivers/gpu/drm/scheduler/sched_entity.c
+++ b/drivers/gpu/drm/scheduler/sched_entity.c
@@ -173,26 +173,15 @@ int drm_sched_entity_error(struct drm_sched_entity *entity)
 }
 EXPORT_SYMBOL(drm_sched_entity_error);
 
+static void drm_sched_entity_kill_jobs_cb(struct dma_fence *f,
+					  struct dma_fence_cb *cb);
+
 static void drm_sched_entity_kill_jobs_work(struct work_struct *wrk)
 {
 	struct drm_sched_job *job = container_of(wrk, typeof(*job), work);
-
-	drm_sched_fence_scheduled(job->s_fence, NULL);
-	drm_sched_fence_finished(job->s_fence, -ESRCH);
-	WARN_ON(job->s_fence->parent);
-	job->sched->ops->free_job(job);
-}
-
-/* Signal the scheduler finished fence when the entity in question is killed. */
-static void drm_sched_entity_kill_jobs_cb(struct dma_fence *f,
-					  struct dma_fence_cb *cb)
-{
-	struct drm_sched_job *job = container_of(cb, struct drm_sched_job,
-						 finish_cb);
+	struct dma_fence *f;
 	unsigned long index;
 
-	dma_fence_put(f);
-
 	/* Wait for all dependencies to avoid data corruptions */
 	xa_for_each(&job->dependencies, index, f) {
 		struct drm_sched_fence *s_fence = to_drm_sched_fence(f);
@@ -220,6 +209,21 @@ static void drm_sched_entity_kill_jobs_cb(struct dma_fence *f,
 		dma_fence_put(f);
 	}
 
+	drm_sched_fence_scheduled(job->s_fence, NULL);
+	drm_sched_fence_finished(job->s_fence, -ESRCH);
+	WARN_ON(job->s_fence->parent);
+	job->sched->ops->free_job(job);
+}
+
+/* Signal the scheduler finished fence when the entity in question is killed. */
+static void drm_sched_entity_kill_jobs_cb(struct dma_fence *f,
+					  struct dma_fence_cb *cb)
+{
+	struct drm_sched_job *job = container_of(cb, struct drm_sched_job,
+						 finish_cb);
+
+	dma_fence_put(f);
+
 	INIT_WORK(&job->work, drm_sched_entity_kill_jobs_work);
 	schedule_work(&job->work);
 }
-- 
2.43.0