drm/amdgpu: Fix deadlock during GPU reset.

Bug:
Kfifo is limited at size, during GPU reset it would fill up to limit
and the pushing thread (producer) would wait for the scheduler worker to
consume the items in the fifo while holding reservation lock
on a BO. The gpu reset thread on the other hand blocks the scheduler
during reset. Before it unblocks the sceduler it might want
to recover VRAM and so will try to reserve the same BO the producer
thread is already holding creating a deadlock.

Fix:
Switch from kfifo to SPSC queue which is unlimited in size.
Signed-off-by: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/scheduler/gpu_sched_trace.h

@@ -29,8 +29,8 @@ TRACE_EVENT(amd_sched_job,
 			   __entry->id = sched_job->id;
 			   __entry->fence = &sched_job->s_fence->finished;
 			   __entry->name = sched_job->sched->name;
-			   __entry->job_count = kfifo_len(
-				   &sched_job->s_entity->job_queue) / sizeof(sched_job);
+			   __entry->job_count = spsc_queue_count(
+				   &sched_job->s_entity->job_queue);
 			   __entry->hw_job_count = atomic_read(
 				   &sched_job->sched->hw_rq_count);
 			   ),

drivers/gpu/drm/amd/scheduler/gpu_scheduler.c

@@ -28,9 +28,14 @@
 #include <drm/drmP.h>
 #include "gpu_scheduler.h"
 
+#include "spsc_queue.h"
+
 #define CREATE_TRACE_POINTS
 #include "gpu_sched_trace.h"
 
+#define to_amd_sched_job(sched_job)		\
+		container_of((sched_job), struct amd_sched_job, queue_node)
+
 static bool amd_sched_entity_is_ready(struct amd_sched_entity *entity);
 static void amd_sched_wakeup(struct amd_gpu_scheduler *sched);
 static void amd_sched_process_job(struct dma_fence *f, struct dma_fence_cb *cb);
@@ -123,8 +128,6 @@ int amd_sched_entity_init(struct amd_gpu_scheduler *sched,
 			  struct amd_sched_rq *rq,
 			  uint32_t jobs, atomic_t *guilty)
 {
-	int r;
-
 	if (!(sched && entity && rq))
 		return -EINVAL;
 
@@ -136,9 +139,7 @@ int amd_sched_entity_init(struct amd_gpu_scheduler *sched,
 
 	spin_lock_init(&entity->rq_lock);
 	spin_lock_init(&entity->queue_lock);
-	r = kfifo_alloc(&entity->job_queue, jobs * sizeof(void *), GFP_KERNEL);
-	if (r)
-		return r;
+	spsc_queue_init(&entity->job_queue);
 
 	atomic_set(&entity->fence_seq, 0);
 	entity->fence_context = dma_fence_context_alloc(2);
@@ -171,7 +172,7 @@ static bool amd_sched_entity_is_initialized(struct amd_gpu_scheduler *sched,
 static bool amd_sched_entity_is_idle(struct amd_sched_entity *entity)
 {
 	rmb();
-	if (kfifo_is_empty(&entity->job_queue))
+	if (spsc_queue_peek(&entity->job_queue) == NULL)
 		return true;
 
 	return false;
@@ -186,7 +187,7 @@ static bool amd_sched_entity_is_idle(struct amd_sched_entity *entity)
  */
 static bool amd_sched_entity_is_ready(struct amd_sched_entity *entity)
 {
-	if (kfifo_is_empty(&entity->job_queue))
+	if (spsc_queue_peek(&entity->job_queue) == NULL)
 		return false;
 
 	if (READ_ONCE(entity->dependency))
@@ -228,7 +229,7 @@ void amd_sched_entity_fini(struct amd_gpu_scheduler *sched,
 		 */
 		kthread_park(sched->thread);
 		kthread_unpark(sched->thread);
-		while (kfifo_out(&entity->job_queue, &job, sizeof(job))) {
+		while ((job = to_amd_sched_job(spsc_queue_pop(&entity->job_queue)))) {
 			struct amd_sched_fence *s_fence = job->s_fence;
 			amd_sched_fence_scheduled(s_fence);
 			dma_fence_set_error(&s_fence->finished, -ESRCH);
@@ -236,9 +237,7 @@ void amd_sched_entity_fini(struct amd_gpu_scheduler *sched,
 			dma_fence_put(&s_fence->finished);
 			sched->ops->free_job(job);
 		}
-
 	}
-	kfifo_free(&entity->job_queue);
 }
 
 static void amd_sched_entity_wakeup(struct dma_fence *f, struct dma_fence_cb *cb)
@@ -333,40 +332,41 @@ static bool amd_sched_entity_add_dependency_cb(struct amd_sched_entity *entity)
 }
 
 static struct amd_sched_job *
-amd_sched_entity_peek_job(struct amd_sched_entity *entity)
+amd_sched_entity_pop_job(struct amd_sched_entity *entity)
 {
 	struct amd_gpu_scheduler *sched = entity->sched;
-	struct amd_sched_job *sched_job;
+	struct amd_sched_job *sched_job = to_amd_sched_job(
+						spsc_queue_peek(&entity->job_queue));
 
-	if (!kfifo_out_peek(&entity->job_queue, &sched_job, sizeof(sched_job)))
+	if (!sched_job)
 		return NULL;
 
 	while ((entity->dependency = sched->ops->dependency(sched_job)))
 		if (amd_sched_entity_add_dependency_cb(entity))
 			return NULL;
 
+	sched_job->s_entity = NULL;
+	spsc_queue_pop(&entity->job_queue);
 	return sched_job;
 }
 
 /**
- * Helper to submit a job to the job queue
+ * Submit a job to the job queue
  *
  * @sched_job		The pointer to job required to submit
  *
- * Returns true if we could submit the job.
+ * Returns 0 for success, negative error code otherwise.
  */
-static bool amd_sched_entity_in(struct amd_sched_job *sched_job)
+void amd_sched_entity_push_job(struct amd_sched_job *sched_job)
 {
 	struct amd_gpu_scheduler *sched = sched_job->sched;
 	struct amd_sched_entity *entity = sched_job->s_entity;
-	bool added, first = false;
+	bool first = false;
 
-	spin_lock(&entity->queue_lock);
-	added = kfifo_in(&entity->job_queue, &sched_job,
-			sizeof(sched_job)) == sizeof(sched_job);
+	trace_amd_sched_job(sched_job);
 
-	if (added && kfifo_len(&entity->job_queue) == sizeof(sched_job))
-		first = true;
+	spin_lock(&entity->queue_lock);
+	first = spsc_queue_push(&entity->job_queue, &sched_job->queue_node);
 
 	spin_unlock(&entity->queue_lock);
 
@@ -378,7 +378,6 @@ static bool amd_sched_entity_in(struct amd_sched_job *sched_job)
 		spin_unlock(&entity->rq_lock);
 		amd_sched_wakeup(sched);
 	}
-	return added;
 }
 
 /* job_finish is called after hw fence signaled
@@ -535,22 +534,6 @@ void amd_sched_job_recovery(struct amd_gpu_scheduler *sched)
 	spin_unlock(&sched->job_list_lock);
 }
 
-/**
- * Submit a job to the job queue
- *
- * @sched_job		The pointer to job required to submit
- *
- * Returns 0 for success, negative error code otherwise.
- */
-void amd_sched_entity_push_job(struct amd_sched_job *sched_job)
-{
-	struct amd_sched_entity *entity = sched_job->s_entity;
-
-	trace_amd_sched_job(sched_job);
-	wait_event(entity->sched->job_scheduled,
-		   amd_sched_entity_in(sched_job));
-}
-
 /* init a sched_job with basic field */
 int amd_sched_job_init(struct amd_sched_job *job,
 		       struct amd_gpu_scheduler *sched,
@@ -641,7 +624,7 @@ static int amd_sched_main(void *param)
 {
 	struct sched_param sparam = {.sched_priority = 1};
 	struct amd_gpu_scheduler *sched = (struct amd_gpu_scheduler *)param;
-	int r, count;
+	int r;
 
 	sched_setscheduler(current, SCHED_FIFO, &sparam);
 
@@ -659,7 +642,7 @@ static int amd_sched_main(void *param)
 		if (!entity)
 			continue;
 
-		sched_job = amd_sched_entity_peek_job(entity);
+		sched_job = amd_sched_entity_pop_job(entity);
 		if (!sched_job)
 			continue;
 
@@ -686,9 +669,6 @@ static int amd_sched_main(void *param)
 			amd_sched_process_job(NULL, &s_fence->cb);
 		}
 
-		count = kfifo_out(&entity->job_queue, &sched_job,
-				sizeof(sched_job));
-		WARN_ON(count != sizeof(sched_job));
 		wake_up(&sched->job_scheduled);
 	}
 	return 0;

drivers/gpu/drm/amd/scheduler/gpu_scheduler.h

@@ -26,6 +26,7 @@
 
 #include <linux/kfifo.h>
 #include <linux/dma-fence.h>
+#include "spsc_queue.h"
 
 struct amd_gpu_scheduler;
 struct amd_sched_rq;
@@ -56,7 +57,7 @@ struct amd_sched_entity {
 	struct amd_gpu_scheduler	*sched;
 
 	spinlock_t			queue_lock;
-	struct kfifo                    job_queue;
+	struct spsc_queue	job_queue;
 
 	atomic_t			fence_seq;
 	uint64_t                        fence_context;
@@ -88,6 +89,7 @@ struct amd_sched_fence {
 };
 
 struct amd_sched_job {
+	struct spsc_node queue_node;
 	struct amd_gpu_scheduler        *sched;
 	struct amd_sched_entity         *s_entity;
 	struct amd_sched_fence          *s_fence;