netdev - Re: [PATCH net-next V2 2/2] net: kfree_skb_list use kmem_cache_free

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CANn89iL_Wi0Qwqg8=X9zO09=eY9srnF8XjmL9t=P9kn=GR_aGw@mail.gmail.com>
Date:   Wed, 18 Jan 2023 17:42:59 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jesper Dangaard Brouer <jbrouer@...hat.com>
Cc:     brouer@...hat.com, netdev@...r.kernel.org,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>, pabeni@...hat.com
Subject: Re: [PATCH net-next V2 2/2] net: kfree_skb_list use kmem_cache_free_bulk

On Wed, Jan 18, 2023 at 5:42 PM Jesper Dangaard Brouer
<jbrouer@...hat.com> wrote:
>
>
> On 18/01/2023 17.05, Eric Dumazet wrote:
> > On Fri, Jan 13, 2023 at 2:52 PM Jesper Dangaard Brouer
> > <brouer@...hat.com> wrote:
> >>
> >> The kfree_skb_list function walks SKB (via skb->next) and frees them
> >> individually to the SLUB/SLAB allocator (kmem_cache). It is more
> >> efficient to bulk free them via the kmem_cache_free_bulk API.
> >>
> >> This patches create a stack local array with SKBs to bulk free while
> >> walking the list. Bulk array size is limited to 16 SKBs to trade off
> >> stack usage and efficiency. The SLUB kmem_cache "skbuff_head_cache"
> >> uses objsize 256 bytes usually in an order-1 page 8192 bytes that is
> >> 32 objects per slab (can vary on archs and due to SLUB sharing). Thus,
> >> for SLUB the optimal bulk free case is 32 objects belonging to same
> >> slab, but runtime this isn't likely to occur.
> >>
> >> The expected gain from using kmem_cache bulk alloc and free API
> >> have been assessed via a microbencmark kernel module[1].
> >>
> >> The module 'slab_bulk_test01' results at bulk 16 element:
> >>   kmem-in-loop Per elem: 109 cycles(tsc) 30.532 ns (step:16)
> >>   kmem-bulk    Per elem: 64 cycles(tsc) 17.905 ns (step:16)
> >>
> >> More detailed description of benchmarks avail in [2].
> >>
> >> [1] https://github.com/netoptimizer/prototype-kernel/tree/master/kernel/mm
> >> [2] https://github.com/xdp-project/xdp-project/blob/master/areas/mem/kfree_skb_list01.org
> >>
> >> V2: rename function to kfree_skb_add_bulk.
> >>
> >> Reviewed-by: Saeed Mahameed <saeed@...nel.org>
> >> Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
> >> ---
> >
> > According to syzbot, this patch causes kernel panics, in IP fragmentation logic.
> >
> > Can you double check if there is no obvious bug ?
>
> Do you have a link to the syzbot issue?

Not yet, I will release it, with a repro.