Re: [PATCH v3] mm/slub: Avoid list corruption when removing a slab from the full list

[David Rientjes <rientjes@google.com>]

On Sat, 12 Oct 2024, yuan.gao wrote:

> On 24/10/11 11:07AM, Christoph Lameter (Ampere) wrote:
> > On Fri, 11 Oct 2024, yuan.gao wrote:
> > 
> > > When an object belonging to the slab got freed later, the remove_full()
> > > function is called. Because the slab is neither on the partial list nor
> > > on the full list, it eventually lead to a list corruption.
> > 
> > We detect list poison....
> > 
> > > diff --git a/mm/slab.h b/mm/slab.h
> > > index 6c6fe6d630ce..7681e71d9a13 100644
> > > --- a/mm/slab.h
> > > +++ b/mm/slab.h
> > > @@ -73,6 +73,10 @@ struct slab {
> > >  						struct {
> > >  							unsigned inuse:16;
> > >  							unsigned objects:15;
> > > +							/*
> > > +							 * Reuse frozen bit for slab with debug enabled:
> > 
> > "If slab debugging is enabled then the frozen bit can bereused to
> >  indicate that the slab was corrupted"
> > 
> > > index 5b832512044e..b9265e9f11aa 100644
> > > --- a/mm/slub.c
> > > +++ b/mm/slub.c
> > > @@ -1423,6 +1423,11 @@ static int check_slab(struct kmem_cache *s, struct slab *slab)
> > >  			slab->inuse, slab->objects);
> > >  		return 0;
> > >  	}
> > > +	if (slab->frozen) {
> > > +		slab_err(s, slab, "Corrupted slab");
> > 
> > 
> > "Slab folio disabled due to metadata corruption" ?
> > 
> > 
> 
> Yes, that's what I meant. 
> Perhaps I should change the description from "Corrupted slab" to
> "Metadata corrupt"?
> 

I think the point here is that slab page corruption is different from slab 
metadata corruption :)

The suggested phrasing, "Slab folio disabled due to metadata corruption", 
sounds good to me.

> > > @@ -2744,7 +2750,10 @@ static void *alloc_single_from_partial(struct kmem_cache *s,
> > >  	slab->inuse++;
> > >
> > >  	if (!alloc_debug_processing(s, slab, object, orig_size)) {
> > > -		remove_partial(n, slab);
> > > +		if (folio_test_slab(slab_folio(slab))) {
> > 
> > 
> > Does folio_test_slab test for the frozen bit??
> > 
> 
> For slab folios, slab->fronzen has been set to 1.
> For non-slab folios, we should not call remove_partial().
> I'm not sure if I understand this correctly.
> 
> Thanks
>