ext4: Fix discard of inode prealloc space with delayed allocation.

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>

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);

fs/ext4/inode.c

@@ -1067,9 +1067,16 @@ static void ext4_da_update_reserve_space(struct inode *inode, int used)
 	/*
 	 * free those over-booking quota for metadata blocks
 	 */
-
 	if (mdb_free)
 		vfs_dq_release_reservation_block(inode, mdb_free);
+
+	/*
+	 * If we have done all the pending block allocations and if
+	 * there aren't any writers on the inode, we can discard the
+	 * inode's preallocations.
+	 */
+	if (!total && (atomic_read(&inode->i_writecount) == 0))
+		ext4_discard_preallocations(inode);
 }
 
 /*