[PATCH] SWDEV-197284 - drm/amdgpu: Only use the peek function in productor side is not correct

[Emily Deng]

For spsc queue, use peek function would cause error in productor side.
As for the last element, when the push job is occurring during pop job, the peek function
will not be updated in time, and it will return NULL.

So use queue count for double confirming the job queue is empty.

Signed-off-by: Emily Deng <Emily.Deng at amd.com>
---
 drivers/gpu/drm/scheduler/sched_entity.c | 4 ++--
 include/drm/spsc_queue.h                 | 7 +++----
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
index 35ddbec..e74894f 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_peek(&entity->job_queue) == NULL) && !spsc_queue_count(&entity->job_queue)))
 		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_peek(&entity->job_queue) == NULL) && !spsc_queue_count(&entity->job_queue)) {
 		if (sched) {
 			/* Park the kernel for a moment to make sure it isn't processing
 			 * our enity.
diff --git a/include/drm/spsc_queue.h b/include/drm/spsc_queue.h
index 125f096..78092b9 100644
--- a/include/drm/spsc_queue.h
+++ b/include/drm/spsc_queue.h
@@ -54,9 +54,8 @@ static inline void spsc_queue_init(struct spsc_queue *queue)
 
 static inline struct spsc_node *spsc_queue_peek(struct spsc_queue *queue)
 {
-	return queue->head;
+	return READ_ONCE(queue->head);
 }
-
 static inline int spsc_queue_count(struct spsc_queue *queue)
 {
 	return atomic_read(&queue->job_count);
@@ -70,9 +69,9 @@ static inline bool spsc_queue_push(struct spsc_queue *queue, struct spsc_node *n
 
 	preempt_disable();
 
+	atomic_inc(&queue->job_count);
 	tail = (struct spsc_node **)atomic_long_xchg(&queue->tail, (long)&node->next);
 	WRITE_ONCE(*tail, node);
-	atomic_inc(&queue->job_count);
 
 	/*
 	 * In case of first element verify new node will be visible to the consumer
@@ -93,6 +92,7 @@ static inline struct spsc_node *spsc_queue_pop(struct spsc_queue *queue)
 	/* Verify reading from memory and not the cache */
 	smp_rmb();
 
+	atomic_dec(&queue->job_count);
 	node = READ_ONCE(queue->head);
 
 	if (!node)
@@ -113,7 +113,6 @@ static inline struct spsc_node *spsc_queue_pop(struct spsc_queue *queue)
 		}
 	}
 
-	atomic_dec(&queue->job_count);
 	return node;
 }
 
-- 
2.7.4