From: Eric Sandeen <sandeen@redhat.com>
Date: Thu, 2 Sep 2010 19:01:44 -0400
Subject: [fs] ext3: flush disk caches on fsync when needed
Message-id: <4C7FF498.80101@redhat.com>
Patchwork-id: 28028
O-Subject: [PATCH RHEL5.6] ext3: Flush disk caches on fsync when needed
Bugzilla: 592961

For:
Bug 592961 - ext3: fsync() does not flush disk caches

Straightforward backport of the following upstream commit.

This will have a significant impact on fsync performance when
barriers are enabled - but remember barriers are not on by
default for ext3 in RHEL5.  This data integrity will have to
come at the cost of performance when barriers are enabled
on a write-back cache device.

There have been subsequent (post-RHEL6) patches upstream which
test whether the journal commit may have already issued a flush,
but it's all a lot more invasive, and I'm not that inclined
to make all those changes now for RHEL5.6.  So just sending this
simple patch.

Thanks,
-Eric

commit 56fcad29d4b3cbcbb2ed47a9d3ceca3f57175417
Author: Jan Kara <jack@suse.cz>
Date:   Tue Sep 8 14:59:42 2009 +0200

    ext3: Flush disk caches on fsync when needed

    In case we fsync() a file and inode is not dirty, we don't force a transaction
    to disk and hence don't flush disk caches. Thus file data could be just in disk
    caches and not on persistent storage. Fix the problem by flushing disk caches
    if we didn't force a transaction commit.

    Signed-off-by: Jan Kara <jack@suse.cz>

Signed-off-by: Jarod Wilson <jarod@redhat.com>

diff --git a/fs/ext3/fsync.c b/fs/ext3/fsync.c
index b98095d..a0f3672 100644
--- a/fs/ext3/fsync.c
+++ b/fs/ext3/fsync.c
@@ -23,6 +23,7 @@
  */
 
 #include <linux/time.h>
+#include <linux/blkdev.h>
 #include <linux/fs.h>
 #include <linux/sched.h>
 #include <linux/writeback.h>
@@ -73,7 +74,7 @@ int ext3_sync_file(struct file * file, struct dentry *dentry, int datasync)
 	}
 
 	if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
-		goto out;
+		goto flush;
 
 	/*
 	 * The VFS has written the file data.  If the inode is unaltered
@@ -85,7 +86,16 @@ int ext3_sync_file(struct file * file, struct dentry *dentry, int datasync)
 			.nr_to_write = 0, /* sys_fsync did this */
 		};
 		ret = sync_inode(inode, &wbc);
+		goto out;
 	}
+flush:
+	/*
+	 * In case we didn't commit a transaction, we have to flush
+	 * disk caches manually so that data really is on persistent
+	 * storage
+	 */
+	if (test_opt(inode->i_sb, BARRIER))
+		blkdev_issue_flush(inode->i_sb->s_bdev, NULL);
 out:
 	return ret;
 }