netdev - Re: 4.6.3, pppoe + shaper workload, skb_panic / skb_push / ppp_start

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Message-ID: <CAM_iQpWuCw6Bgm=1BWMkoFkuav5xV+FyKPq0Ef+3N_qpQqv=AA@mail.gmail.com>
Date:	Tue, 12 Jul 2016 10:31:18 -0700
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	nuclearcat@...learcat.com
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: 4.6.3, pppoe + shaper workload, skb_panic / skb_push / ppp_start_xmit

On Mon, Jul 11, 2016 at 12:45 PM,  <nuclearcat@...learcat.com> wrote:
> Hi
>
> On latest kernel i noticed kernel panic happening 1-2 times per day. It is
> also happening on older kernel (at least 4.5.3).
>
...
>  [42916.426463] Call Trace:
>  [42916.426658]  <IRQ>
>
>  [42916.426719]  [<ffffffff81843786>] skb_push+0x36/0x37
>  [42916.427111]  [<ffffffffa00e8ce5>] ppp_start_xmit+0x10f/0x150
> [ppp_generic]
>  [42916.427314]  [<ffffffff81853467>] dev_hard_start_xmit+0x25a/0x2d3
>  [42916.427516]  [<ffffffff818530f2>] ?
> validate_xmit_skb.isra.107.part.108+0x11d/0x238
>  [42916.427858]  [<ffffffff8186dee3>] sch_direct_xmit+0x89/0x1b5
>  [42916.428060]  [<ffffffff8186e142>] __qdisc_run+0x133/0x170
>  [42916.428261]  [<ffffffff81850034>] net_tx_action+0xe3/0x148
>  [42916.428462]  [<ffffffff810c401a>] __do_softirq+0xb9/0x1a9
>  [42916.428663]  [<ffffffff810c4251>] irq_exit+0x37/0x7c
>  [42916.428862]  [<ffffffff8102b8f7>] smp_apic_timer_interrupt+0x3d/0x48
>  [42916.429063]  [<ffffffff818cb15c>] apic_timer_interrupt+0x7c/0x90

Interesting, we call a skb_cow_head() before skb_push() in ppp_start_xmit(),
I have no idea why this could happen.

Do you have any tc qdisc, filter or actions on this ppp device?