Re: [PATCH] kmemleak: Avoid RCU stalls when freeing metadata for per-CPU pointers

Catalin Marinas
2023-12-06T11:22:30Z

On Sat, Dec 02, 2023 at 03:50:55PM +0800, Hillf Danton wrote:
> On Fri, 1 Dec 2023 19:08:29 +0000 Catalin Marinas <catalin.marinas@arm.com>
> > @@ -1472,14 +1474,27 @@ static void scan_object(struct kmemleak_object *object)
> > /* already freed object */
> > goto out;
> >
> > - obj_ptr = object->flags & OBJECT_PHYS ?
> > - __va((phys_addr_t)object->pointer) :
> > - (void *)object->pointer;
> > + if (object->flags & OBJECT_PERCPU) {
> > + unsigned int cpu;
> >
> > - if (hlist_empty(&object->area_list) ||
> > + for_each_possible_cpu(cpu) {
> > + void *start = per_cpu_ptr((void __percpu *)object->pointer, cpu);
> > + void *end = start + object->size;
> > +
> > + scan_block(start, end, object);
> > +
> > + raw_spin_unlock_irqrestore(&object->lock, flags);
> > + cond_resched();
> > + raw_spin_lock_irqsave(&object->lock, flags);
>
> Nit, spin_lock/unlock can be collapsed into need_resched().
>
> if (need_resched()) {
> raw_spin_unlock_irqrestore(&object->lock, flags);
> cond_resched();
> raw_spin_lock_irqsave(&object->lock, flags);
> }

The reason I'd not do this is that we also want the interrupts to be
re-enabled regularly. Keeping them disabled may not even mark the
current thread as need_resched().

--
Catalin