[PATCH,STABLE 2.6.29 08/18] ext4: Fix discard of inode prealloc space with delayed allocation.

[Theodore Ts'o <tytso@mit.edu>]

From: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

With delayed allocation we should not/cannot discard inode prealloc
space during file close. We would still have dirty pages for which we
haven't allocated blocks yet. With this fix after each get_blocks
request we check whether we have zero reserved blocks and if yes and
we don't have any writers on the file we discard inode prealloc space.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
(cherry picked from commit d6014301b5599fba395c42a1e96a7fe86f7d0b2d)
---
 fs/ext4/file.c  |    3 ++-
 fs/ext4/inode.c |    9 ++++++++-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 06df827..588af8c 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -39,7 +39,8 @@ static int ext4_release_file(struct inode *inode, struct file *filp)
 	}
 	/* if we are the last writer on the inode, drop the block reservation */
 	if ((filp->f_mode & FMODE_WRITE) &&
-			(atomic_read(&inode->i_writecount) == 1))
+			(atomic_read(&inode->i_writecount) == 1) &&
+		        !EXT4_I(inode)->i_reserved_data_blocks)
 	{
 		down_write(&EXT4_I(inode)->i_data_sem);
 		ext4_discard_preallocations(inode);
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 8c7259a..3dafa6b 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1036,8 +1036,15 @@ static void ext4_da_update_reserve_space(struct inode *inode, int used)
 	/* update per-inode reservations */
 	BUG_ON(used  > EXT4_I(inode)->i_reserved_data_blocks);
 	EXT4_I(inode)->i_reserved_data_blocks -= used;