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Message-ID: <Zfho1lRIg0cjpWwK@google.com>
Date: Mon, 18 Mar 2024 09:16:22 -0700
From: Stanislav Fomichev <sdf@...gle.com>
To: Daniele Salvatore Albano <d.albano@...il.com>
Cc: netdev@...r.kernel.org
Subject: Re: [mlx5_core] kernel NULL pointer dereference when sending packets
with AF_XDP using the hw checksum
On 03/16, Daniele Salvatore Albano wrote:
> On Sat, 16 Mar 2024 at 05:11, Stanislav Fomichev <sdf@...gle.com> wrote:
> >
> > On 03/16, Daniele Salvatore Albano wrote:
> > > Hey there,
> > >
> > > Hope this is the right ml, if not sorry in advance.
> > >
> > > I have been facing a reproducible kernel panic with 6.8.0 and 6.8.1
> > > when sending packets and enabling the HW checksum calculation with
> > > AF_XDP on my mellanox connect 5.
> > >
> > > Running xskgen ( https://github.com/fomichev/xskgen ), which I saw
> > > mentioned in some patches related to AF_XDP and the hw checksum
> > > support. In addition to the minimum parameters to make it work, adding
> > > the -m option is enough to trigger the kernel panic.
> >
> > Now I wonder if I ever tested only -m (without passing a flag to request
> > tx timestamp). Maybe you can try to confirm that `xskgen -mC` works?
>
> No, the kernel panics and, from the look of it, the stack trace and
> the RIP are the same.
>
> [ 157.108402] RIP: 0010:mlx5e_free_xdpsq_desc+0x266/0x320 [mlx5_core]
> ...
> [ 157.108827] Call Trace:
> [ 157.108841] <TASK>
> [ 157.108855] ? show_regs+0x6d/0x80
> [ 157.108876] ? __die+0x24/0x80
> [ 157.108893] ? page_fault_oops+0x99/0x1b0
> [ 157.108916] ? do_user_addr_fault+0x2ee/0x6b0
> [ 157.108937] ? exc_page_fault+0x83/0x1b0
> [ 157.108958] ? asm_exc_page_fault+0x27/0x30
> [ 157.108986] ? mlx5e_free_xdpsq_desc+0x266/0x320 [mlx5_core]
> [ 157.109154] mlx5e_poll_xdpsq_cq+0x17c/0x4f0 [mlx5_core]
> [ 157.109324] mlx5e_napi_poll+0x45e/0x7b0 [mlx5_core]
> [ 157.109470] __napi_poll+0x33/0x200
> [ 157.109488] net_rx_action+0x181/0x2e0
> [ 157.109502] ? sched_clock_cpu+0x12/0x1e0
> [ 157.109524] __do_softirq+0xe1/0x363
> [ 157.109544] ? __pfx_smpboot_thread_fn+0x10/0x10
> [ 157.109565] run_ksoftirqd+0x37/0x60
> [ 157.109582] smpboot_thread_fn+0xe3/0x1e0
> [ 157.109600] kthread+0xf2/0x120
> [ 157.109616] ? __pfx_kthread+0x10/0x10
> [ 157.109632] ret_from_fork+0x47/0x70
> [ 157.109648] ? __pfx_kthread+0x10/0x10
> [ 157.109663] ret_from_fork_asm+0x1b/0x30
> [ 157.109686] </TASK>
>
> > If you can test custom patches, I think the following should fix it:
> >
> > diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
> > index 3cb4dc9bd70e..3d54de168a6d 100644
> > --- a/include/net/xdp_sock.h
> > +++ b/include/net/xdp_sock.h
> > @@ -188,6 +188,8 @@ static inline void xsk_tx_metadata_complete(struct xsk_tx_metadata_compl *compl,
> > {
> > if (!compl)
> > return;
> > + if (!compl->tx_timestamp)
> > + return;
> >
> > *compl->tx_timestamp = ops->tmo_fill_timestamp(priv);
> > }
>
> Just built the same kernel from mainline ubuntu 6.8.1 with the patch
> applied and it now works with both xsk and my code.
Thanks, will send this fix shortly!
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