jbd2: finish conversion from WRITE_SYNC_PLUG to WRITE_SYNC and explicit plugging

'write_op' was still used, even though it was always WRITE_SYNC now.
Add plugging around the cases where it submits IO, and flush them
before we end up waiting for that IO.
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

fs/jbd2/commit.c

@@ -329,7 +329,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
 	int tag_bytes = journal_tag_bytes(journal);
 	struct buffer_head *cbh = NULL; /* For transactional checksums */
 	__u32 crc32_sum = ~0;
-	int write_op = WRITE_SYNC;
+	struct blk_plug plug;
 
 	/*
 	 * First job: lock down the current transaction and wait for
@@ -363,13 +363,6 @@ void jbd2_journal_commit_transaction(journal_t *journal)
 	write_lock(&journal->j_state_lock);
 	commit_transaction->t_state = T_LOCKED;
 
-	/*
-	 * Use plugged writes here, since we want to submit several before
-	 * we unplug the device. We don't do explicit unplugging in here,
-	 * instead we rely on sync_buffer() doing the unplug for us.
-	 */
-	if (commit_transaction->t_synchronous_commit)
-		write_op = WRITE_SYNC;
 	trace_jbd2_commit_locking(journal, commit_transaction);
 	stats.run.rs_wait = commit_transaction->t_max_wait;
 	stats.run.rs_locked = jiffies;
@@ -469,8 +462,10 @@ void jbd2_journal_commit_transaction(journal_t *journal)
 	if (err)
 		jbd2_journal_abort(journal, err);
 
+	blk_start_plug(&plug);
 	jbd2_journal_write_revoke_records(journal, commit_transaction,
-					  write_op);
+					  WRITE_SYNC);
+	blk_finish_plug(&plug);
 
 	jbd_debug(3, "JBD: commit phase 2\n");
 
@@ -497,6 +492,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
 	err = 0;
 	descriptor = NULL;
 	bufs = 0;
+	blk_start_plug(&plug);
 	while (commit_transaction->t_buffers) {
 
 		/* Find the next buffer to be journaled... */
@@ -658,7 +654,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
 				clear_buffer_dirty(bh);
 				set_buffer_uptodate(bh);
 				bh->b_end_io = journal_end_buffer_io_sync;
-				submit_bh(write_op, bh);
+				submit_bh(WRITE_SYNC, bh);
 			}
 			cond_resched();
 			stats.run.rs_blocks_logged += bufs;
@@ -699,6 +695,8 @@ void jbd2_journal_commit_transaction(journal_t *journal)
 			__jbd2_journal_abort_hard(journal);
 	}
 
+	blk_finish_plug(&plug);
+
 	/* Lo and behold: we have just managed to send a transaction to
            the log.  Before we can commit it, wait for the IO so far to
            complete.  Control buffers being written are on the