Btrfs: Add a per-inode csum mutex to avoid races creating csum items

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index 5ba8389..40b4e0c 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -30,6 +30,7 @@
 	struct extent_map_tree extent_tree;
 	struct extent_io_tree io_tree;
 	struct extent_io_tree io_failure_tree;
+	struct mutex csum_mutex;
 	struct inode vfs_inode;
 	atomic_t ordered_writeback;