ext4: fix cache flish in ext4_sync_file

We need to flush the write cache unconditionally in ->fsync, otherwise writes into already allocated blocks can get lost. Writes into fully allocated files are very common when using disk images for virtualization, and without this fix can easily lose data after an fdatasync, which is the typical implementation for a cache flush on the virtual drive.

Signed-off-by Christoph Hellwig <[email protected]>

Index: linux-2.6/fs/ext4/fsync.c
===================================================================

fs/ext4/fsync.c +2 -3

@@ -92,9 +92,9 @@ int ext4_sync_file(struct file *file, st
 			.nr_to_write = 0, /* sys_fsync did this */
 		};
 		ret = sync_inode(inode, &wbc);
-		if (journal && (journal->j_flags & JBD2_BARRIER))
-			blkdev_issue_flush(inode->i_sb->s_bdev, NULL);
 	}
 out:
+	if (journal && (journal->j_flags & JBD2_BARRIER))
+		blkdev_issue_flush(inode->i_sb->s_bdev, NULL);
 	return ret;
 }
--

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Quoted 8 lines · Christoph Hellwig

We need to flush the write cache unconditionally in ->fsync, otherwise writes into already allocated blocks can get lost. Writes into fully allocated files are very common when using disk images for virtualization, and without this fix can easily lose data after an fdatasync, which is the typical implementation for a cache flush on the virtual drive.

Quoted 1 line

Signed-off-by Christoph Hellwig <[email protected]>

Fixing my old commit, I guess ;)