ext4: Fix possible recursive locking warning in EXT4_IOC_MOVE_EXT

ext4: Fix possible recursive locking warning in EXT4_IOC_MOVE_EXT

From: Akira Fujita <[email protected]>

If kernel configuration related to lock debugging is enabled, we get possible recursive locking warning. Therefore, use down_write_nested() to guarantee
the lock order explicitly.

This problem has been reported by Brian Rogers before.
http://marc.info/?l=linux-ext4&m=125115356928011&w=1

---
 fs/ext4/move_extent.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

index a7410b3..2ca6aa3 100644
@@ -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);
 }
 
 /**

Thanks, I've added this patch to the ext4 patch queue, but with the following updated commit description:

ext4: Fix possible recursive locking warning in EXT4_IOC_MOVE_EXT

From: Akira Fujita <[email protected]>

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