linux-kernel - Re: [PATCH v4 bpf-next 1/3] bpf: Add kmem

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Message-ID: <CAPhsuW5BKxZH2EA=fuQa_3man5_qcUt3euwtfwsqD4g36JngaA@mail.gmail.com>
Date: Fri, 4 Oct 2024 13:45:09 -0700
From: Song Liu <song@...nel.org>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Yonghong Song <yonghong.song@...ux.dev>, 
	John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, 
	Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	LKML <linux-kernel@...r.kernel.org>, bpf@...r.kernel.org, 
	Andrew Morton <akpm@...ux-foundation.org>, Christoph Lameter <cl@...ux.com>, 
	Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, 
	Joonsoo Kim <iamjoonsoo.kim@....com>, Vlastimil Babka <vbabka@...e.cz>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Hyeonggon Yoo <42.hyeyoo@...il.com>, linux-mm@...ck.org, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Kees Cook <kees@...nel.org>
Subject: Re: [PATCH v4 bpf-next 1/3] bpf: Add kmem_cache iterator

On Wed, Oct 2, 2024 at 11:09 AM Namhyung Kim <namhyung@...nel.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)
[...]