Re: [PATCH 1/3] mm/slub: fix the race between validate_slab and slab_free

[Rongwei Wang]

On 6/8/22 8:23 PM, Christoph Lameter wrote:
> On Wed, 8 Jun 2022, Rongwei Wang wrote:
>
> > If available, I think document the issue and warn this incorrect behavior is
> > OK. But it still prints a large amount of confusing messages, and disturbs us?
>
> Correct it would be great if you could fix this in a way that does not
> impact performance.
>
> > > are current operations on the slab being validated.
> > And I am trying to fix it in following way. In a short, these changes only
> > works under the slub debug mode, and not affects the normal mode (I'm not
> > sure). It looks not elegant enough. And if all approve of this way, I can
> > submit the next version.
>
>
> > Anyway, thanks for your time:).
> > -wrw
> >
> > @@ -3304,7 +3300,7 @@ static void __slab_free(struct kmem_cache *s,
> struct
> > slab *slab,
> >
> >   {
> >          void *prior;
> > -       int was_frozen;
> > +       int was_frozen, to_take_off = 0;
> >          struct slab new;
>
> to_take_off has the role of !n ? Why is that needed?
>
> > -       do {
> > -               if (unlikely(n)) {
> > +               spin_lock_irqsave(&n->list_lock, flags);
> > +               ret = free_debug_processing(s, slab, head, tail, cnt, addr);
>
> Ok so the idea is to take the lock only if kmem_cache_debug. That looks
> ok. But it still adds a number of new branches etc to the free loop.
>
> Some performance tests would be useful.
Hi Christoph

Thanks for your time!
Do you have some advice in benchmarks that need me to test? And I find 
that hackbench and lkp was used frequently in mm/slub.c commits[1,2]. 
But I have no idea how to use these two benchmarks test to cover the 
above changes. Can you give some examples? Thanks very much!

Sorry for late reply!

[1]https://lore.kernel.org/lkml/20210301080404.GF12822@xsang-OptiPlex-9020/
[2]https://lore.kernel.org/linux-mm/20210128134512.GF3592@xxxxxxxxxxxxxxxxxxx/