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

[Namhyung Kim <namhyung@kernel.org>]

On Fri, Oct 04, 2024 at 01:45:09PM -0700, Song Liu wrote:
> On Wed, Oct 2, 2024 at 11:09 AM Namhyung Kim <namhyung@kernel.org> wrote:
> >
> [...]
> > +
> > +static void *kmem_cache_iter_seq_start(struct seq_file *seq, loff_t *pos)
> > +{
> > +       loff_t cnt = 0;
> > +       bool found = false;
> > +       struct kmem_cache *s;
> > +
> > +       mutex_lock(&slab_mutex);
> > +
> > +       /*
> > +        * Find an entry at the given position in the slab_caches list instead
> > +        * of keeping a reference (of the last visited entry, if any) out of
> > +        * slab_mutex. It might miss something if one is deleted in the middle
> > +        * while it releases the lock.  But it should be rare and there's not
> > +        * much we can do about it.
> > +        */
> > +       list_for_each_entry(s, &slab_caches, list) {
> > +               if (cnt == *pos) {
> > +                       /*
> > +                        * Make sure this entry remains in the list by getting
> > +                        * a new reference count.  Note that boot_cache entries
> > +                        * have a negative refcount, so don't touch them.
> > +                        */
> > +                       if (s->refcount > 0)
> > +                               s->refcount++;
> > +                       found = true;
> > +                       break;
> > +               }
> > +               cnt++;
> > +       }
> > +       mutex_unlock(&slab_mutex);
> > +
> > +       if (!found)
> > +               return NULL;
> > +
> > +       ++*pos;
> 
> This should be
> 
> if (*pos == 0)
>     ++*pos;

Oh, I thought there's check for seq->count after the seq->op->show()
for the ->start().  I need to check this logic again, thanks for
pointing this out.

Thanks,
Namhyung

> 
> > +       return s;
> > +}
> > +
> > +static void kmem_cache_iter_seq_stop(struct seq_file *seq, void *v)
> [...]