lockd: ensure we use the correct file descriptor when unlocking

Shared locks are set on O_RDONLY descriptors and exclusive locks are set
on O_WRONLY ones. nlmsvc_unlock however calls vfs_lock_file twice, once
for each descriptor, but it doesn't reset fl_file. Ensure that it does.
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/lockd/svclock.c

@@ -659,11 +659,13 @@ nlmsvc_unlock(struct net *net, struct nlm_file *file, struct nlm_lock *lock)
 	nlmsvc_cancel_blocked(net, file, lock);
 
 	lock->fl.fl_type = F_UNLCK;
-	if (file->f_file[O_RDONLY])
-		error = vfs_lock_file(file->f_file[O_RDONLY], F_SETLK,
+	lock->fl.fl_file = file->f_file[O_RDONLY];
+	if (lock->fl.fl_file)
+		error = vfs_lock_file(lock->fl.fl_file, F_SETLK,
 					&lock->fl, NULL);
-	if (file->f_file[O_WRONLY])
-		error = vfs_lock_file(file->f_file[O_WRONLY], F_SETLK,
+	lock->fl.fl_file = file->f_file[O_WRONLY];
+	if (lock->fl.fl_file)
+		error |= vfs_lock_file(lock->fl.fl_file, F_SETLK,
 					&lock->fl, NULL);
 
 	return (error < 0)? nlm_lck_denied_nolocks : nlm_granted;