drm/shmem-helper: Use refcount_t for vmap_use_count

Use refcount_t helper for vmap_use_count to make refcounting consistent
with pages_use_count and pages_pin_count that use refcount_t. This also
makes vmapping to benefit from the refcount_t's overflow checks.

Acked-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>

drivers/gpu/drm/drm_gem_shmem_helper.c

@@ -165,7 +165,7 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
 	} else {
 		dma_resv_lock(shmem->base.resv, NULL);
 
-		drm_WARN_ON(obj->dev, shmem->vmap_use_count);
+		drm_WARN_ON(obj->dev, refcount_read(&shmem->vmap_use_count));
 
 		if (shmem->sgt) {
 			dma_unmap_sgtable(obj->dev->dev, shmem->sgt,
@@ -355,23 +355,25 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
 
 		dma_resv_assert_held(shmem->base.resv);
 
-		if (shmem->vmap_use_count++ > 0) {
+		if (refcount_inc_not_zero(&shmem->vmap_use_count)) {
 			iosys_map_set_vaddr(map, shmem->vaddr);
 			return 0;
 		}
 
 		ret = drm_gem_shmem_pin_locked(shmem);
 		if (ret)
-			goto err_zero_use;
+			return ret;
 
 		if (shmem->map_wc)
 			prot = pgprot_writecombine(prot);
 		shmem->vaddr = vmap(shmem->pages, obj->size >> PAGE_SHIFT,
 				    VM_MAP, prot);
-		if (!shmem->vaddr)
+		if (!shmem->vaddr) {
 			ret = -ENOMEM;
-		else
+		} else {
 			iosys_map_set_vaddr(map, shmem->vaddr);
+			refcount_set(&shmem->vmap_use_count, 1);
+		}
 	}
 
 	if (ret) {
@@ -384,8 +386,6 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
 err_put_pages:
 	if (!drm_gem_is_imported(obj))
 		drm_gem_shmem_unpin_locked(shmem);
-err_zero_use:
-	shmem->vmap_use_count = 0;
 
 	return ret;
 }
@@ -413,14 +413,10 @@ void drm_gem_shmem_vunmap_locked(struct drm_gem_shmem_object *shmem,
 	} else {
 		dma_resv_assert_held(shmem->base.resv);
 
-		if (drm_WARN_ON_ONCE(obj->dev, !shmem->vmap_use_count))
-			return;
-
-		if (--shmem->vmap_use_count > 0)
-			return;
-
-		vunmap(shmem->vaddr);
-		drm_gem_shmem_unpin_locked(shmem);
+		if (refcount_dec_and_test(&shmem->vmap_use_count)) {
+			vunmap(shmem->vaddr);
+			drm_gem_shmem_unpin_locked(shmem);
+		}
 	}
 
 	shmem->vaddr = NULL;
@@ -672,7 +668,7 @@ void drm_gem_shmem_print_info(const struct drm_gem_shmem_object *shmem,
 
 	drm_printf_indent(p, indent, "pages_pin_count=%u\n", refcount_read(&shmem->pages_pin_count));
 	drm_printf_indent(p, indent, "pages_use_count=%u\n", refcount_read(&shmem->pages_use_count));
-	drm_printf_indent(p, indent, "vmap_use_count=%u\n", shmem->vmap_use_count);
+	drm_printf_indent(p, indent, "vmap_use_count=%u\n", refcount_read(&shmem->vmap_use_count));
 	drm_printf_indent(p, indent, "vaddr=%p\n", shmem->vaddr);
 }
 EXPORT_SYMBOL_GPL(drm_gem_shmem_print_info);

drivers/gpu/drm/tests/drm_gem_shmem_test.c

@@ -168,7 +168,7 @@ static void drm_gem_shmem_test_vmap(struct kunit *test)
 	shmem = drm_gem_shmem_create(drm_dev, TEST_SIZE);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, shmem);
 	KUNIT_EXPECT_NULL(test, shmem->vaddr);
-	KUNIT_EXPECT_EQ(test, shmem->vmap_use_count, 0);
+	KUNIT_EXPECT_EQ(test, refcount_read(&shmem->vmap_use_count), 0);
 
 	ret = kunit_add_action_or_reset(test, drm_gem_shmem_free_wrapper, shmem);
 	KUNIT_ASSERT_EQ(test, ret, 0);
@@ -177,7 +177,7 @@ static void drm_gem_shmem_test_vmap(struct kunit *test)
 	KUNIT_ASSERT_EQ(test, ret, 0);
 	KUNIT_ASSERT_NOT_NULL(test, shmem->vaddr);
 	KUNIT_ASSERT_FALSE(test, iosys_map_is_null(&map));
-	KUNIT_EXPECT_EQ(test, shmem->vmap_use_count, 1);
+	KUNIT_EXPECT_EQ(test, refcount_read(&shmem->vmap_use_count), 1);
 
 	iosys_map_memset(&map, 0, TEST_BYTE, TEST_SIZE);
 	for (i = 0; i < TEST_SIZE; i++)
@@ -185,7 +185,7 @@ static void drm_gem_shmem_test_vmap(struct kunit *test)
 
 	drm_gem_shmem_vunmap_locked(shmem, &map);
 	KUNIT_EXPECT_NULL(test, shmem->vaddr);
-	KUNIT_EXPECT_EQ(test, shmem->vmap_use_count, 0);
+	KUNIT_EXPECT_EQ(test, refcount_read(&shmem->vmap_use_count), 0);
 }
 
 /*

include/drm/drm_gem_shmem_helper.h

@@ -82,7 +82,7 @@ struct drm_gem_shmem_object {
 	 * Reference count on the virtual address.
 	 * The address are un-mapped when the count reaches zero.
 	 */
-	unsigned int vmap_use_count;
+	refcount_t vmap_use_count;
 
 	/**
 	 * @pages_mark_dirty_on_put: