dma-buf: further relax reservation_object_add_shared_fence

Other cores don't busy wait any more and we removed the last user of checking
the seqno for changes. Drop updating the number for shared fences altogether.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/322379/?series=64837&rev=1

drivers/dma-buf/reservation.c

@@ -237,9 +237,6 @@ void reservation_object_add_shared_fence(struct reservation_object *obj,
 	fobj = reservation_object_get_list(obj);
 	count = fobj->shared_count;
 
-	preempt_disable();
-	write_seqcount_begin(&obj->seq);
-
 	for (i = 0; i < count; ++i) {
 
 		old = rcu_dereference_protected(fobj->shared[i],
@@ -257,9 +254,6 @@ replace:
 	RCU_INIT_POINTER(fobj->shared[i], fence);
 	/* pointer update must be visible before we extend the shared_count */
 	smp_store_mb(fobj->shared_count, count);
-
-	write_seqcount_end(&obj->seq);
-	preempt_enable();
 	dma_fence_put(old);
 }
 EXPORT_SYMBOL(reservation_object_add_shared_fence);

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

@@ -251,12 +251,7 @@ static int amdgpu_amdkfd_remove_eviction_fence(struct amdgpu_bo *bo,
 	new->shared_max = old->shared_max;
 	new->shared_count = k;
 
-	/* Install the new fence list, seqcount provides the barriers */
-	preempt_disable();
-	write_seqcount_begin(&resv->seq);
-	RCU_INIT_POINTER(resv->fence, new);
-	write_seqcount_end(&resv->seq);
-	preempt_enable();
+	rcu_assign_pointer(resv->fence, new);
 
 	/* Drop the references to the removed fences or move them to ef_list */
 	for (i = j, k = 0; i < old->shared_count; ++i) {