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>

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;
 }