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

[yuan.gao]

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"?

> > @@ -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