dma-buf: rename and cleanup dma_resv_get_excl v3

When the comment needs to state explicitly that this
doesn't get a reference to the object then the function
is named rather badly.

Rename the function and use rcu_dereference_check(), this
way it can be used from both rcu as well as lock protected
critical sections.

v2: improve kerneldoc as suggested by Daniel
v3: use dma_resv_excl_fence as function name
Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20210602111714.212426-4-christian.koenig@amd.com

drivers/dma-buf/dma-buf.c

@@ -234,7 +234,7 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
 		shared_count = fobj->shared_count;
 	else
 		shared_count = 0;
-	fence_excl = rcu_dereference(resv->fence_excl);
+	fence_excl = dma_resv_excl_fence(resv);
 	if (read_seqcount_retry(&resv->seq, seq)) {
 		rcu_read_unlock();
 		goto retry;
@@ -1382,8 +1382,7 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)
 				buf_obj->name ?: "");
 
 		robj = buf_obj->resv;
-		fence = rcu_dereference_protected(robj->fence_excl,
-						  dma_resv_held(robj));
+		fence = dma_resv_excl_fence(robj);
 		if (fence)
 			seq_printf(s, "\tExclusive fence: %s %s %ssignalled\n",
 				   fence->ops->get_driver_name(fence),

drivers/dma-buf/dma-resv.c

@@ -284,7 +284,7 @@ EXPORT_SYMBOL(dma_resv_add_shared_fence);
  */
 void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence)
 {
-	struct dma_fence *old_fence = dma_resv_get_excl(obj);
+	struct dma_fence *old_fence = dma_resv_excl_fence(obj);
 	struct dma_resv_list *old;
 	u32 i = 0;
 
@@ -380,7 +380,7 @@ int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src)
 	rcu_read_unlock();
 
 	src_list = dma_resv_get_list(dst);
-	old = dma_resv_get_excl(dst);
+	old = dma_resv_excl_fence(dst);
 
 	write_seqcount_begin(&dst->seq);
 	/* write_seqcount_begin provides the necessary memory barrier */
@@ -428,7 +428,7 @@ int dma_resv_get_fences_rcu(struct dma_resv *obj,
 		rcu_read_lock();
 		seq = read_seqcount_begin(&obj->seq);
 
-		fence_excl = rcu_dereference(obj->fence_excl);
+		fence_excl = dma_resv_excl_fence(obj);
 		if (fence_excl && !dma_fence_get_rcu(fence_excl))
 			goto unlock;
 
@@ -523,7 +523,7 @@ long dma_resv_wait_timeout_rcu(struct dma_resv *obj,
 	rcu_read_lock();
 	i = -1;
 
-	fence = rcu_dereference(obj->fence_excl);
+	fence = dma_resv_excl_fence(obj);
 	if (fence && !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
 		if (!dma_fence_get_rcu(fence))
 			goto unlock_retry;
@@ -645,7 +645,7 @@ bool dma_resv_test_signaled_rcu(struct dma_resv *obj, bool test_all)
 	}
 
 	if (!shared_count) {
-		struct dma_fence *fence_excl = rcu_dereference(obj->fence_excl);
+		struct dma_fence *fence_excl = dma_resv_excl_fence(obj);
 
 		if (fence_excl) {
 			ret = dma_resv_test_signaled_single(fence_excl);

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

@@ -226,7 +226,7 @@ static void amdgpu_gem_object_close(struct drm_gem_object *obj,
 	if (!amdgpu_vm_ready(vm))
 		goto out_unlock;
 
-	fence = dma_resv_get_excl(bo->tbo.base.resv);
+	fence = dma_resv_excl_fence(bo->tbo.base.resv);
 	if (fence) {
 		amdgpu_bo_fence(bo, fence, true);
 		fence = NULL;

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

@@ -210,7 +210,7 @@ int amdgpu_sync_resv(struct amdgpu_device *adev, struct amdgpu_sync *sync,
 		return -EINVAL;
 
 	/* always sync to the exclusive fence */
-	f = dma_resv_get_excl(resv);
+	f = dma_resv_excl_fence(resv);
 	r = amdgpu_sync_fence(sync, f);
 
 	flist = dma_resv_get_list(resv);

drivers/gpu/drm/etnaviv/etnaviv_gem.c

@@ -471,7 +471,7 @@ static void etnaviv_gem_describe(struct drm_gem_object *obj, struct seq_file *m)
 		}
 	}
 
-	fence = rcu_dereference(robj->fence_excl);
+	fence = dma_resv_excl_fence(robj);
 	if (fence)
 		etnaviv_gem_describe_fence(fence, "Exclusive", m);
 	rcu_read_unlock();

drivers/gpu/drm/i915/gem/i915_gem_busy.c

@@ -113,8 +113,7 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
 	seq = raw_read_seqcount(&obj->base.resv->seq);
 
 	/* Translate the exclusive fence to the READ *and* WRITE engine */
-	args->busy =
-		busy_check_writer(rcu_dereference(obj->base.resv->fence_excl));
+	args->busy = busy_check_writer(dma_resv_excl_fence(obj->base.resv));
 
 	/* Translate shared fences to READ set of engines */
 	list = rcu_dereference(obj->base.resv->fence);

drivers/gpu/drm/msm/msm_gem.c

@@ -819,7 +819,7 @@ int msm_gem_sync_object(struct drm_gem_object *obj,
 
 	fobj = dma_resv_get_list(obj->resv);
 	if (!fobj || (fobj->shared_count == 0)) {
-		fence = dma_resv_get_excl(obj->resv);
+		fence = dma_resv_excl_fence(obj->resv);
 		/* don't need to wait on our own fences, since ring is fifo */
 		if (fence && (fence->context != fctx->context)) {
 			ret = dma_fence_wait(fence, true);
@@ -1035,7 +1035,7 @@ void msm_gem_describe(struct drm_gem_object *obj, struct seq_file *m,
 		}
 	}
 
-	fence = rcu_dereference(robj->fence_excl);
+	fence = dma_resv_excl_fence(robj);
 	if (fence)
 		describe_fence(fence, "Exclusive", m);
 	rcu_read_unlock();

drivers/gpu/drm/nouveau/nouveau_bo.c

@@ -951,7 +951,7 @@ nouveau_bo_vm_cleanup(struct ttm_buffer_object *bo,
 {
 	struct nouveau_drm *drm = nouveau_bdev(bo->bdev);
 	struct drm_device *dev = drm->dev;
-	struct dma_fence *fence = dma_resv_get_excl(bo->base.resv);
+	struct dma_fence *fence = dma_resv_excl_fence(bo->base.resv);
 
 	nv10_bo_put_tile_region(dev, *old_tile, fence);
 	*old_tile = new_tile;

drivers/gpu/drm/nouveau/nouveau_fence.c

@@ -356,7 +356,7 @@ nouveau_fence_sync(struct nouveau_bo *nvbo, struct nouveau_channel *chan, bool e
 	}
 
 	fobj = dma_resv_get_list(resv);
-	fence = dma_resv_get_excl(resv);
+	fence = dma_resv_excl_fence(resv);
 
 	if (fence && (!exclusive || !fobj || !fobj->shared_count)) {
 		struct nouveau_channel *prev = NULL;

drivers/gpu/drm/radeon/radeon_display.c

@@ -533,7 +533,7 @@ static int radeon_crtc_page_flip_target(struct drm_crtc *crtc,
 		DRM_ERROR("failed to pin new rbo buffer before flip\n");
 		goto cleanup;
 	}
-	work->fence = dma_fence_get(dma_resv_get_excl(new_rbo->tbo.base.resv));
+	work->fence = dma_fence_get(dma_resv_excl_fence(new_rbo->tbo.base.resv));
 	radeon_bo_get_tiling_flags(new_rbo, &tiling_flags, NULL);
 	radeon_bo_unreserve(new_rbo);
 

drivers/gpu/drm/radeon/radeon_sync.c

@@ -98,7 +98,7 @@ int radeon_sync_resv(struct radeon_device *rdev,
 	int r = 0;
 
 	/* always sync to the exclusive fence */
-	f = dma_resv_get_excl(resv);
+	f = dma_resv_excl_fence(resv);
 	fence = f ? to_radeon_fence(f) : NULL;
 	if (fence && fence->rdev == rdev)
 		radeon_sync_fence(sync, fence);

drivers/gpu/drm/radeon/radeon_uvd.c

@@ -477,7 +477,7 @@ static int radeon_uvd_cs_msg(struct radeon_cs_parser *p, struct radeon_bo *bo,
 		return -EINVAL;
 	}
 
-	f = dma_resv_get_excl(bo->tbo.base.resv);
+	f = dma_resv_excl_fence(bo->tbo.base.resv);
 	if (f) {
 		r = radeon_fence_wait((struct radeon_fence *)f, false);
 		if (r) {

drivers/gpu/drm/ttm/ttm_bo.c

@@ -262,7 +262,7 @@ static void ttm_bo_flush_all_fences(struct ttm_buffer_object *bo)
 
 	rcu_read_lock();
 	fobj = rcu_dereference(resv->fence);
-	fence = rcu_dereference(resv->fence_excl);
+	fence = dma_resv_excl_fence(resv);
 	if (fence && !fence->ops->signaled)
 		dma_fence_enable_sw_signaling(fence);
 

drivers/gpu/drm/vmwgfx/vmwgfx_resource.c

@@ -1166,7 +1166,7 @@ int vmw_resources_clean(struct vmw_buffer_object *vbo, pgoff_t start,
 		if (bo->moving)
 			dma_fence_put(bo->moving);
 		bo->moving = dma_fence_get
-			(dma_resv_get_excl(bo->base.resv));
+			(dma_resv_excl_fence(bo->base.resv));
 	}
 
 	return 0;

include/linux/dma-resv.h

@@ -226,22 +226,20 @@ static inline void dma_resv_unlock(struct dma_resv *obj)
 }
 
 /**
- * dma_resv_get_excl - get the reservation object's
- * exclusive fence, with update-side lock held
+ * dma_resv_exclusive - return the object's exclusive fence
  * @obj: the reservation object
  *
- * Returns the exclusive fence (if any).  Does NOT take a
- * reference. Writers must hold obj->lock, readers may only
- * hold a RCU read side lock.
+ * Returns the exclusive fence (if any). Caller must either hold the objects
+ * through dma_resv_lock() or the RCU read side lock through rcu_read_lock(),
+ * or one of the variants of each
  *
  * RETURNS
  * The exclusive fence or NULL
  */
 static inline struct dma_fence *
-dma_resv_get_excl(struct dma_resv *obj)
+dma_resv_excl_fence(struct dma_resv *obj)
 {
-	return rcu_dereference_protected(obj->fence_excl,
-					 dma_resv_held(obj));
+	return rcu_dereference_check(obj->fence_excl, dma_resv_held(obj));
 }
 
 /**