pick_link(): take reserving space on stack into a new helper

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -1580,22 +1580,15 @@ static inline int may_lookup(struct nameidata *nd)
 	return inode_permission(nd->inode, MAY_EXEC);
 }
 
-enum {WALK_TRAILING = 1, WALK_MORE = 2, WALK_NOFOLLOW = 4};
-
-static const char *pick_link(struct nameidata *nd, struct path *link,
-		     struct inode *inode, unsigned seq, int flags)
+static int reserve_stack(struct nameidata *nd, struct path *link, unsigned seq)
 {
-	struct saved *last;
-	const char *res;
 	int error;
 
-	if (unlikely(nd->total_link_count++ >= MAXSYMLINKS)) {
-		if (!(nd->flags & LOOKUP_RCU))
-			path_put(link);
-		return ERR_PTR(-ELOOP);
-	}
+	if (unlikely(nd->total_link_count++ >= MAXSYMLINKS))
+		return -ELOOP;
 	error = nd_alloc_stack(nd);
-	if (unlikely(error)) {
+	if (likely(!error))
+		return 0;
 	if (error == -ECHILD) {
 		// we must grab link first
 		bool grabbed_link = legitimize_path(nd, link, seq);
@@ -1606,12 +1599,23 @@ static const char *pick_link(struct nameidata *nd, struct path *link,
 		if (!error)
 			error = nd_alloc_stack(nd);
 	}
-		if (error) {
+	return error;
+}
+
+enum {WALK_TRAILING = 1, WALK_MORE = 2, WALK_NOFOLLOW = 4};
+
+static const char *pick_link(struct nameidata *nd, struct path *link,
+		     struct inode *inode, unsigned seq, int flags)
+{
+	struct saved *last;
+	const char *res;
+	int error = reserve_stack(nd, link, seq);
+
+	if (unlikely(error)) {
+		if (!(nd->flags & LOOKUP_RCU))
 			path_put(link);
 		return ERR_PTR(error);
 	}
-	}
-
 	last = nd->stack + nd->depth++;
 	last->link = *link;
 	clear_delayed_call(&last->done);