btrfs: push errors up from add_async_extent()

The memory allocation error in add_async_extent() is not handled
properly, return an error and push the BUG_ON to the caller. Handling it
there is not trivial so at least make it visible.
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -738,7 +738,8 @@ static noinline int add_async_extent(struct async_chunk *cow,
 	struct async_extent *async_extent;
 
 	async_extent = kmalloc(sizeof(*async_extent), GFP_NOFS);
-	BUG_ON(!async_extent); /* -ENOMEM */
+	if (!async_extent)
+		return -ENOMEM;
 	async_extent->start = start;
 	async_extent->ram_size = ram_size;
 	async_extent->compressed_size = compressed_size;
@@ -1025,8 +1026,9 @@ static void compress_file_range(struct btrfs_work *work)
 	 * The async work queues will take care of doing actual allocation on
 	 * disk for these compressed pages, and will submit the bios.
 	 */
-	add_async_extent(async_chunk, start, total_in, total_compressed, pages,
-			 nr_pages, compress_type);
+	ret = add_async_extent(async_chunk, start, total_in, total_compressed, pages,
+			       nr_pages, compress_type);
+	BUG_ON(ret);
 	if (start + total_in < end) {
 		start += total_in;
 		cond_resched();
@@ -1038,8 +1040,9 @@ static void compress_file_range(struct btrfs_work *work)
 	if (!btrfs_test_opt(fs_info, FORCE_COMPRESS) && !inode->prop_compress)
 		inode->flags |= BTRFS_INODE_NOCOMPRESS;
 cleanup_and_bail_uncompressed:
-	add_async_extent(async_chunk, start, end - start + 1, 0, NULL, 0,
-			 BTRFS_COMPRESS_NONE);
+	ret = add_async_extent(async_chunk, start, end - start + 1, 0, NULL, 0,
+			       BTRFS_COMPRESS_NONE);
+	BUG_ON(ret);
 free_pages:
 	if (pages) {
 		for (i = 0; i < nr_pages; i++) {