jbd2: Modify ASYNC_COMMIT code to not rely on queue draining on barrier

Currently JBD2 relies blkdev_issue_flush() draining the queue when ASYNC_COMMIT
feature is set. This property is going away so make JBD2 wait for buffers it
needs on its own before submitting the cache flush.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

fs/jbd2/commit.c

@@ -701,6 +701,16 @@ start_journal_io:
 		}
 	}
 
+	err = journal_finish_inode_data_buffers(journal, commit_transaction);
+	if (err) {
+		printk(KERN_WARNING
+			"JBD2: Detected IO errors while flushing file data "
+		       "on %s\n", journal->j_devname);
+		if (journal->j_flags & JBD2_ABORT_ON_SYNCDATA_ERR)
+			jbd2_journal_abort(journal, err);
+		err = 0;
+	}
+
 	/* 
 	 * If the journal is not located on the file system device,
 	 * then we must flush the file system device before we issue
@@ -719,19 +729,6 @@ start_journal_io:
 						 &cbh, crc32_sum);
 		if (err)
 			__jbd2_journal_abort_hard(journal);
-		if (journal->j_flags & JBD2_BARRIER)
-			blkdev_issue_flush(journal->j_dev, GFP_KERNEL, NULL,
-				BLKDEV_IFL_WAIT);
-	}
-
-	err = journal_finish_inode_data_buffers(journal, commit_transaction);
-	if (err) {
-		printk(KERN_WARNING
-			"JBD2: Detected IO errors while flushing file data "
-		       "on %s\n", journal->j_devname);
-		if (journal->j_flags & JBD2_ABORT_ON_SYNCDATA_ERR)
-			jbd2_journal_abort(journal, err);
-		err = 0;
 	}
 
 	/* Lo and behold: we have just managed to send a transaction to
@@ -845,6 +842,12 @@ wait_for_iobuf:
 	}
 	if (!err && !is_journal_aborted(journal))
 		err = journal_wait_on_commit_record(journal, cbh);
+	if (JBD2_HAS_INCOMPAT_FEATURE(journal,
+				      JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT) &&
+	    journal->j_flags & JBD2_BARRIER) {
+		blkdev_issue_flush(journal->j_dev, GFP_KERNEL, NULL,
+				   BLKDEV_IFL_WAIT);
+	}
 
 	if (err)
 		jbd2_journal_abort(journal, err);