jbd: 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: NJens Axboe <jaxboe@fusionio.com>

fs/jbd/commit.c

@@ -20,6 +20,7 @@
 #include <linux/mm.h>
 #include <linux/pagemap.h>
 #include <linux/bio.h>
+#include <linux/blkdev.h>
 
 /*
  * Default IO end handler for temporary BJ_IO buffer_heads.
@@ -294,7 +295,7 @@ void journal_commit_transaction(journal_t *journal)
 	int first_tag = 0;
 	int tag_flag;
 	int i;
-	int write_op = WRITE_SYNC;
+	struct blk_plug plug;
 
 	/*
 	 * First job: lock down the current transaction and wait for
@@ -327,13 +328,6 @@ void journal_commit_transaction(journal_t *journal)
 	spin_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;
 	spin_lock(&commit_transaction->t_handle_lock);
 	while (commit_transaction->t_updates) {
 		DEFINE_WAIT(wait);
@@ -418,8 +412,10 @@ void journal_commit_transaction(journal_t *journal)
 	 * Now start flushing things to disk, in the order they appear
 	 * on the transaction lists.  Data blocks go first.
 	 */
+	blk_start_plug(&plug);
 	err = journal_submit_data_buffers(journal, commit_transaction,
-					  write_op);
+					  WRITE_SYNC);
+	blk_finish_plug(&plug);
 
 	/*
 	 * Wait for all previously submitted IO to complete.
@@ -480,7 +476,9 @@ void journal_commit_transaction(journal_t *journal)
 		err = 0;
 	}
 
-	journal_write_revoke_records(journal, commit_transaction, write_op);
+	blk_start_plug(&plug);
+
+	journal_write_revoke_records(journal, commit_transaction, WRITE_SYNC);
 
 	/*
 	 * If we found any dirty or locked buffers, then we should have
@@ -650,7 +648,7 @@ void 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();
 
@@ -661,6 +659,8 @@ void journal_commit_transaction(journal_t *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