ext4: fix possible recursive locking warning in EXT4_IOC_MOVE_EXT

(cherry picked from commit 49bd22bc4d603a2a4fc2a6a60e156cbea52eb494)

If CONFIG_PROVE_LOCKING is enabled, the double_down_write_data_sem()
will trigger a false-positive warning of a recursive lock.  Since we
take i_data_sem for the two inodes ordered by their inode numbers,
this isn't a problem.  Use of down_write_nested() will notify the lock
dependency checker machinery that there is no problem here.

This problem was reported by Brian Rogers:

	http://marc.info/?l=linux-ext4&m=125115356928011&w=1

Reported-by: Brian Rogers <brian@xyzw.org>
Signed-off-by: Akira Fujita <a-fujita@rs.jp.nec.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
index 3ec76110373d1df2d2f6717d4f00007c56d9ff92..db8508fc9858fe76f3bb086d2ce6258c214bf68f 100644 (file)
--- a/fs/ext4/move_extent.c
+++ b/fs/ext4/move_extent.c
@@ -189,7 +189,7 @@ double_down_write_data_sem(struct inode *orig_inode, struct inode *donor_inode)
        }
 
        down_write(&EXT4_I(first)->i_data_sem);
-       down_write(&EXT4_I(second)->i_data_sem);
+       down_write_nested(&EXT4_I(second)->i_data_sem, SINGLE_DEPTH_NESTING);
 }
 
 /**