btrfs: Factor out common extent locking code in submit_compressed_extents

Irrespective of whether the compress code fell back to uncompressed or
a compressed extent has to be submitted, the extent range is always
locked. So factor out the common lock_extent call at the beginning of
the loop. No functional changes just removes one duplicate lock_extent
call.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -725,16 +725,15 @@ static noinline void submit_compressed_extents(struct async_chunk *async_chunk)
 		async_extent = list_entry(async_chunk->extents.next,
 					  struct async_extent, list);
 		list_del(&async_extent->list);
+
 retry:
+		lock_extent(io_tree, async_extent->start,
+			    async_extent->start + async_extent->ram_size - 1);
 		/* did the compression code fall back to uncompressed IO? */
 		if (!async_extent->pages) {
 			int page_started = 0;
 			unsigned long nr_written = 0;
 
-			lock_extent(io_tree, async_extent->start,
-					 async_extent->start +
-					 async_extent->ram_size - 1);
-
 			/* allocate blocks */
 			ret = cow_file_range(inode, async_chunk->locked_page,
 					     async_extent->start,
@@ -766,9 +765,6 @@ static noinline void submit_compressed_extents(struct async_chunk *async_chunk)
 			continue;
 		}
 
-		lock_extent(io_tree, async_extent->start,
-			    async_extent->start + async_extent->ram_size - 1);
-
 		ret = btrfs_reserve_extent(root, async_extent->ram_size,
 					   async_extent->compressed_size,
 					   async_extent->compressed_size,