ext4: Initialize fsync transaction ids in ext4_new_inode()

When allocating a new inode, we need to make sure i_sync_tid and
i_datasync_tid are initialized.  Otherwise, one or both of these two
values could be left initialized to zero, which could potentially
result in BUG_ON in jbd2_journal_commit_transaction.

(This could happen by having journal->commit_request getting set to
zero, which could wake up the kjournald process even though there is
no running transaction, which then causes a BUG_ON via the 
J_ASSERT(j_ruinning_transaction != NULL) statement.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/ialloc.c

@@ -1054,6 +1054,11 @@ struct inode *ext4_new_inode(handle_t *handle, struct inode *dir, int mode,
 		}
 	}
 
+	if (ext4_handle_valid(handle)) {
+		ei->i_sync_tid = handle->h_transaction->t_tid;
+		ei->i_datasync_tid = handle->h_transaction->t_tid;
+	}
+
 	err = ext4_mark_inode_dirty(handle, inode);
 	if (err) {
 		ext4_std_error(sb, err);