[PATCH] jbd2: wait for already submitted t_sync_datalist buffer to complete

In the current jbd code, if a buffer on BJ_SyncData list is dirty and not
locked, the buffer is refiled to BJ_Locked list, submitted to the IO and
waited for IO completion.

But the fsstress test showed the case that when a buffer was already
submitted to the IO just before the buffer_dirty(bh) check, the buffer was
not waited for IO completion.

Following patch solves this problem.  If it is assumed that a buffer is
submitted to the IO before the buffer_dirty(bh) check and still being
written to disk, this buffer is refiled to BJ_Locked list.
Signed-off-by: NHisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp>
Cc: Jan Kara <jack@ucw.cz>
Cc: "Stephen C. Tweedie" <sct@redhat.com>
Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

fs/jbd2/commit.c

@@ -248,8 +248,12 @@ static void journal_submit_data_buffers(journal_t *journal,
 				bufs = 0;
 				goto write_out_data;
 			}
-		}
-		else {
+		} else if (!locked && buffer_locked(bh)) {
+			__jbd2_journal_file_buffer(jh, commit_transaction,
+						BJ_Locked);
+			jbd_unlock_bh_state(bh);
+			put_bh(bh);
+		} else {
 			BUFFER_TRACE(bh, "writeout complete: unfile");
 			__jbd2_journal_unfile_buffer(jh);
 			jbd_unlock_bh_state(bh);