ocfs2: invalidate dentry if its dentry_lock isn't initialized.

In commit a5a0a630, when
ocfs2_attch_dentry_lock fails, we call an extra iput and reset
dentry->d_fsdata to NULL. This resolve a bug, but it isn't
completed and the dentry is still there. When we want to use
it again, ocfs2_dentry_revalidate doesn't catch it and return
true. That make future ocfs2_dentry_lock panic out.
One bug is http://oss.oracle.com/bugzilla/show_bug.cgi?id=1162.

The resolution is to add a check for dentry->d_fsdata in
revalidate process and return false if dentry->d_fsdata is NULL,
so that a new ocfs2_lookup will be called again.
Signed-off-by: Tao Ma <tao.ma@oracle.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>

fs/ocfs2/dcache.c

@@ -85,6 +85,17 @@ static int ocfs2_dentry_revalidate(struct dentry *dentry,
 		goto bail;
 	}
 
+	/*
+	 * If the last lookup failed to create dentry lock, let us
+	 * redo it.
+	 */
+	if (!dentry->d_fsdata) {
+		mlog(0, "Inode %llu doesn't have dentry lock, "
+		     "returning false\n",
+		     (unsigned long long)OCFS2_I(inode)->ip_blkno);
+		goto bail;
+	}
+
 	ret = 1;
 
 bail: