drm/amdgpu: fix incorrect mutex usage v3

Before this patch the scheduler fence was created when we push the job
into the queue, so we could only get the fence after pushing it.

The mutex now was necessary to prevent the thread pushing the jobs to
the hardware from running faster than the thread pushing the jobs into
the queue.

Otherwise the thread pushing jobs into the queue would have accessed
possible freed up memory when it tries to get a reference to the fence.

So what you get in the end is thread A:
mutex_lock(&job->lock);
...
Kick of thread B.
...
mutex_unlock(&job->lock);

And thread B:
mutex_lock(&job->lock);
....
mutex_unlock(&job->lock);
kfree(job);

I'm actually not sure if I'm still up to date on this, but this usage
pattern used to be not allowed with mutexes. See here as well
https://lwn.net/Articles/575460/.

v2: remove unrelated changes, fix missing owner
v3: rebased, add more commit message

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu.h

@@ -1225,7 +1225,7 @@ struct amdgpu_job {
 	struct amdgpu_device	*adev;
 	struct amdgpu_ib	*ibs;
 	uint32_t		num_ibs;
-	struct mutex            job_lock;
+	void			*owner;
 	struct amdgpu_user_fence uf;
 	int (*free_job)(struct amdgpu_job *job);
 };

drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c

@@ -845,8 +845,9 @@ int amdgpu_cs_ioctl(struct drm_device *dev, void *data, struct drm_file *filp)
 		goto out;
 
 	if (amdgpu_enable_scheduler && parser.num_ibs) {
-		struct amdgpu_job *job;
 		struct amdgpu_ring * ring = parser.ibs->ring;
+		struct amd_sched_fence *fence;
+		struct amdgpu_job *job;
 
 		job = kzalloc(sizeof(struct amdgpu_job), GFP_KERNEL);
 		if (!job) {
@@ -859,37 +860,41 @@ int amdgpu_cs_ioctl(struct drm_device *dev, void *data, struct drm_file *filp)
 		job->adev = parser.adev;
 		job->ibs = parser.ibs;
 		job->num_ibs = parser.num_ibs;
-		job->base.owner = parser.filp;
-		mutex_init(&job->job_lock);
+		job->owner = parser.filp;
+		job->free_job = amdgpu_cs_free_job;
+
 		if (job->ibs[job->num_ibs - 1].user) {
 			job->uf = parser.uf;
 			job->ibs[job->num_ibs - 1].user = &job->uf;
 			parser.uf.bo = NULL;
 		}
 
-		parser.ibs = NULL;
-		parser.num_ibs = 0;
-
-		job->free_job = amdgpu_cs_free_job;
-		mutex_lock(&job->job_lock);
-		r = amd_sched_entity_push_job(&job->base);
-		if (r) {
-			mutex_unlock(&job->job_lock);
+		fence = amd_sched_fence_create(job->base.s_entity,
+					       parser.filp);
+		if (!fence) {
+			r = -ENOMEM;
 			amdgpu_cs_free_job(job);
 			kfree(job);
 			goto out;
 		}
-		cs->out.handle =
-			amdgpu_ctx_add_fence(parser.ctx, ring,
-					     &job->base.s_fence->base);
+		job->base.s_fence = fence;
+		fence_get(&fence->base);
+
+		cs->out.handle = amdgpu_ctx_add_fence(parser.ctx, ring,
+						      &fence->base);
 		job->ibs[job->num_ibs - 1].sequence = cs->out.handle;
 
-		list_sort(NULL, &parser.validated, cmp_size_smaller_first);
-		ttm_eu_fence_buffer_objects(&parser.ticket,
-				&parser.validated,
-				&job->base.s_fence->base);
+		parser.ibs = NULL;
+		parser.num_ibs = 0;
+
 		trace_amdgpu_cs_ioctl(job);
-		mutex_unlock(&job->job_lock);
+		amd_sched_entity_push_job(&job->base);
+
+		list_sort(NULL, &parser.validated, cmp_size_smaller_first);
+		ttm_eu_fence_buffer_objects(&parser.ticket, &parser.validated,
+					    &fence->base);
+		fence_put(&fence->base);
+
 		amdgpu_cs_parser_fini_late(&parser);
 		mutex_unlock(&vm->mutex);
 		return 0;

drivers/gpu/drm/amd/amdgpu/amdgpu_sched.c

@@ -45,12 +45,8 @@ static struct fence *amdgpu_sched_run_job(struct amd_sched_job *sched_job)
 		return NULL;
 	}
 	job = to_amdgpu_job(sched_job);
-	mutex_lock(&job->job_lock);
 	trace_amdgpu_sched_run_job(job);
-	r = amdgpu_ib_schedule(job->adev,
-			       job->num_ibs,
-			       job->ibs,
-			       job->base.owner);
+	r = amdgpu_ib_schedule(job->adev, job->num_ibs, job->ibs, job->owner);
 	if (r) {
 		DRM_ERROR("Error scheduling IBs (%d)\n", r);
 		goto err;
@@ -63,7 +59,6 @@ err:
 	if (job->free_job)
 		job->free_job(job);
 
-	mutex_unlock(&job->job_lock);
 	kfree(job);
 	return fence ? &fence->base : NULL;
 }
@@ -89,21 +84,19 @@ int amdgpu_sched_ib_submit_kernel_helper(struct amdgpu_device *adev,
 			return -ENOMEM;
 		job->base.sched = &ring->sched;
 		job->base.s_entity = &adev->kernel_ctx.rings[ring->idx].entity;
+		job->base.s_fence = amd_sched_fence_create(job->base.s_entity, owner);
+		if (!job->base.s_fence) {
+			kfree(job);
+			return -ENOMEM;
+		}
+		*f = fence_get(&job->base.s_fence->base);
+
 		job->adev = adev;
 		job->ibs = ibs;
 		job->num_ibs = num_ibs;
-		job->base.owner = owner;
-		mutex_init(&job->job_lock);
+		job->owner = owner;
 		job->free_job = free_job;
-		mutex_lock(&job->job_lock);
-		r = amd_sched_entity_push_job(&job->base);
-		if (r) {
-			mutex_unlock(&job->job_lock);
-			kfree(job);
-			return r;
-		}
-		*f = fence_get(&job->base.s_fence->base);
-		mutex_unlock(&job->job_lock);
+		amd_sched_entity_push_job(&job->base);
 	} else {
 		r = amdgpu_ib_schedule(adev, num_ibs, ibs, owner);
 		if (r)

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

@@ -276,21 +276,13 @@ static bool amd_sched_entity_in(struct amd_sched_job *sched_job)
  *
  * Returns 0 for success, negative error code otherwise.
  */
-int amd_sched_entity_push_job(struct amd_sched_job *sched_job)
+void amd_sched_entity_push_job(struct amd_sched_job *sched_job)
 {
 	struct amd_sched_entity *entity = sched_job->s_entity;
-	struct amd_sched_fence *fence = amd_sched_fence_create(
-		entity, sched_job->owner);
-
-	if (!fence)
-		return -ENOMEM;
-
-	sched_job->s_fence = fence;
 
 	wait_event(entity->sched->job_scheduled,
 		   amd_sched_entity_in(sched_job));
 	trace_amd_sched_job(sched_job);
-	return 0;
 }
 
 /**

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

@@ -79,7 +79,6 @@ struct amd_sched_job {
 	struct amd_gpu_scheduler        *sched;
 	struct amd_sched_entity         *s_entity;
 	struct amd_sched_fence          *s_fence;
-	void		                *owner;
 };
 
 extern const struct fence_ops amd_sched_fence_ops;
@@ -131,7 +130,7 @@ int amd_sched_entity_init(struct amd_gpu_scheduler *sched,
 			  uint32_t jobs);
 void amd_sched_entity_fini(struct amd_gpu_scheduler *sched,
 			   struct amd_sched_entity *entity);
-int amd_sched_entity_push_job(struct amd_sched_job *sched_job);
+void amd_sched_entity_push_job(struct amd_sched_job *sched_job);
 
 struct amd_sched_fence *amd_sched_fence_create(
 	struct amd_sched_entity *s_entity, void *owner);