vfree: don't schedule free_work() if llist_add() returns false

vfree() only needs schedule_work(&p->wq) if p->list was empty, otherwise
vfree_deferred->wq is already pending or it is running and didn't do
llist_del_all() yet.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmalloc.c

@@ -1477,7 +1477,6 @@ static void __vunmap(const void *addr, int deallocate_pages)
  *	conventions for vfree() arch-depenedent would be a really bad idea)
  *
  *	NOTE: assumes that the object at *addr has a size >= sizeof(llist_node)
- *	
  */
 void vfree(const void *addr)
 {
@@ -1489,8 +1488,8 @@ void vfree(const void *addr)
 		return;
 	if (unlikely(in_interrupt())) {
 		struct vfree_deferred *p = &__get_cpu_var(vfree_deferred);
-		llist_add((struct llist_node *)addr, &p->list);
-		schedule_work(&p->wq);
+		if (llist_add((struct llist_node *)addr, &p->list))
+			schedule_work(&p->wq);
 	} else
 		__vunmap(addr, 1);
 }