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

[Song Liu <song@kernel.org>]

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;

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