ext4: discard preallocation when restarting a transaction during truncate

When restart a transaction during a truncate operation, we drop and
reacquire i_data_sem.  After reacquiring i_data_sem, we need to
discard any inode-based preallocation that might have been grabbed
while we released i_data_sem (for example, if pdflush is allocating
blocks and racing against the truncate).
Signed-off-by: NAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>

fs/ext4/inode.c

@@ -193,7 +193,7 @@ static int try_to_extend_transaction(handle_t *handle, struct inode *inode)
  * so before we call here everything must be consistently dirtied against
  * this transaction.
  */
- int ext4_truncate_restart_trans(handle_t *handle, struct inode *inode,
+int ext4_truncate_restart_trans(handle_t *handle, struct inode *inode,
 				 int nblocks)
 {
 	int ret;
@@ -209,6 +209,7 @@ static int try_to_extend_transaction(handle_t *handle, struct inode *inode)
 	up_write(&EXT4_I(inode)->i_data_sem);
 	ret = ext4_journal_restart(handle, blocks_for_truncate(inode));
 	down_write(&EXT4_I(inode)->i_data_sem);
+	ext4_discard_preallocations(inode);
 
 	return ret;
 }