ceph: do not set r_old_dentry_dir on link()

This is racy--we do not know whather d_parent has changed out from
underneath us because i_mutex is not held on the source inode's directory.

Also, taking this reference is useless.
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Yan, Zheng <zheng.z.yan@intel.com>

fs/ceph/dir.c

@@ -812,8 +812,7 @@ static int ceph_link(struct dentry *old_dentry, struct inode *dir,
 	}
 	req->r_dentry = dget(dentry);
 	req->r_num_caps = 2;
-	req->r_old_dentry = dget(old_dentry); /* or inode? hrm. */
-	req->r_old_dentry_dir = ceph_get_dentry_parent_inode(old_dentry);
+	req->r_old_dentry = dget(old_dentry);
 	req->r_locked_dir = dir;
 	req->r_dentry_drop = CEPH_CAP_FILE_SHARED;
 	req->r_dentry_unless = CEPH_CAP_FILE_EXCL;