nfsd: Fix error cleanup path in nfsd_rename()

BugLink: https://bugs.launchpad.net/bugs/2065400

[ Upstream commit 9fe6e9e7b58944037714442384075c17cfde1c56 ]

Commit a8b0026847 ("rename(): avoid a deadlock in the case of parents
having no common ancestor") added an error bail out path. However this
path does not drop the remount protection that has been acquired. Fix
the cleanup path to properly drop the remount protection.

Fixes: a8b0026847 ("rename(): avoid a deadlock in the case of parents having no common ancestor")
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Manuel Diewald <manuel.diewald@canonical.com>
Signed-off-by: Roxana Nicolescu <roxana.nicolescu@canonical.com>

fs/nfsd/vfs.c

@@ -1833,7 +1833,7 @@ retry:
 	trap = lock_rename(tdentry, fdentry);
 	if (IS_ERR(trap)) {
 		err = (rqstp->rq_vers == 2) ? nfserr_acces : nfserr_xdev;
-		goto out;
+		goto out_want_write;
 	}
 	err = fh_fill_pre_attrs(ffhp);
 	if (err != nfs_ok)
@@ -1903,6 +1903,7 @@ retry:
 	}
 out_unlock:
 	unlock_rename(tdentry, fdentry);
+out_want_write:
 	fh_drop_write(ffhp);
 
 	/*