On Tue, Jun 14, 2022 at 06:15:14PM +0100, Catalin Marinas wrote:
> On Sun, Jun 12, 2022 at 02:33:01PM -0400, Waiman Long wrote:
> > @@ -1437,10 +1440,25 @@ static void kmemleak_scan(void)
> > #endif
> > /* reset the reference count (whiten the object) */
> > object->count = 0;
> > - if (color_gray(object) && get_object(object))
> > + if (color_gray(object) && get_object(object)) {
> > list_add_tail(&object->gray_list, &gray_list);
> > + gray_list_cnt++;
> > + object_pinned = true;
> > + }
> >
> > raw_spin_unlock_irq(&object->lock);
> > +
> > + /*
> > + * With object pinned by a positive reference count, it
> > + * won't go away and we can safely release the RCU read
> > + * lock and do a cond_resched() to avoid soft lockup every
> > + * 64k objects.
> > + */
> > + if (object_pinned && !(gray_list_cnt & 0xffff)) {
> > + rcu_read_unlock();
> > + cond_resched();
> > + rcu_read_lock();
> > + }
>
> I'm not sure this gains much. There should be very few gray objects
> initially (those passed to kmemleak_not_leak() for example). The
> majority should be white objects.
>
> If we drop the fine-grained object->lock, we could instead take
> kmemleak_lock outside the loop with a cond_resched_lock(&kmemleak_lock)
> within the loop. I think we can get away with not having an
> rcu_read_lock() at all for list traversal with the big lock outside the
> loop.
Actually this doesn't work is the current object in the iteration is
freed. Does list_for_each_rcu_safe() help?
--
Catalin
