Re: [PATCH v4 bpf-next 1/3] bpf: Add kmem_cache iterator

[Namhyung Kim <namhyung@kernel.org>]

On Fri, Oct 04, 2024 at 02:46:43PM -0700, Song Liu wrote:
> On Fri, Oct 4, 2024 at 2:37 PM Namhyung Kim <namhyung@kernel.org> wrote:
> >
> > Hi Song,
> >
> > On Fri, Oct 04, 2024 at 01:33:19PM -0700, Song Liu wrote:
> [...]
> > > > +
> > > > +static void *kmem_cache_iter_seq_next(struct seq_file *seq, void *v, loff_t *pos)
> > > > +{
> > > > +       struct kmem_cache *s = v;
> > > > +       struct kmem_cache *next = NULL;
> > > > +       bool destroy = false;
> > > > +
> > > > +       ++*pos;
> > > > +
> > > > +       mutex_lock(&slab_mutex);
> > > > +
> > > > +       if (list_last_entry(&slab_caches, struct kmem_cache, list) != s) {
> > > > +               next = list_next_entry(s, list);
> > > > +               if (next->refcount > 0)
> > > > +                       next->refcount++;
> > >
> > > What if next->refcount <=0? Shall we find next of next?
> >
> > The slab_mutex should protect refcount == 0 case so it won't see that.
> > The negative refcount means it's a boot_cache and we shouldn't touch the
> > refcount.
> 
> I see. Thanks for the explanation!
> 
> Please add a comment here, and maybe also add
> 
>   WARN_ON_ONCE(next ->refcount == 0).

Sure, thanks for your review!
Namhyung