LOOKUP_MOUNTPOINT: we are cleaning "jumped" flag too late

That (and traversals in case of umount .) should be done before
complete_walk().  Either a braino or mismerge damage on queue
reorders - either way, I should've spotted that much earlier.
Fucked-up-by: Al Viro <viro@zeniv.linux.org.uk>
X-Paperbag: Brown
Fixes: 161aff1d "LOOKUP_MOUNTPOINT: fold path_mountpointat() into path_lookupat()"
Cc: stable@vger.kernel.org # v5.7+
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -2421,16 +2421,16 @@ static int path_lookupat(struct nameidata *nd, unsigned flags, struct path *path
 	while (!(err = link_path_walk(s, nd)) &&
 	       (s = lookup_last(nd)) != NULL)
 		;
+	if (!err && unlikely(nd->flags & LOOKUP_MOUNTPOINT)) {
+		err = handle_lookup_down(nd);
+		nd->flags &= ~LOOKUP_JUMPED; // no d_weak_revalidate(), please...
+	}
 	if (!err)
 		err = complete_walk(nd);
 
 	if (!err && nd->flags & LOOKUP_DIRECTORY)
 		if (!d_can_lookup(nd->path.dentry))
 			err = -ENOTDIR;
-	if (!err && unlikely(nd->flags & LOOKUP_MOUNTPOINT)) {
-		err = handle_lookup_down(nd);
-		nd->flags &= ~LOOKUP_JUMPED; // no d_weak_revalidate(), please...
-	}
 	if (!err) {
 		*path = nd->path;
 		nd->path.mnt = NULL;