netdev - Re: Crash in __netif_receive

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Date:	Wed, 28 Mar 2012 22:01:49 -0500
From:	Avleen Vig <avleen@...il.com>
To:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: Crash in __netif_receive_skb

On Wed, Mar 28, 2012 at 8:31 PM, Avleen Vig <avleen@...il.com> wrote:
> Hi folks, someone in #kernel recommended I email these two lists. Hope
> they're the right place.
>
> We're running 2.6.32-220.4.1.el6.x86_64 on Centos 6.2, and getting a
> repeated crash:
>    https://gist.github.com/2231998
>
> We can make this happen pretty easily just by passing some network
> traffic and waiting a while.
> I couldn't find any references to this particular issue.
> I have vmcore files and am happy to dig into it if it would help (as
> long as someone can tell me what to do :))

I hope this debugging is legit, I'm really new to this level of insight.

I think the problem is in include/linux/netpoll.h, at the "if"
statement at line 86:
    static inline int netpoll_receive_skb(struct sk_buff *skb)
    {
        if (!list_empty(&skb->dev->napi_list))
                return netpoll_rx(skb);
        return 0;
    }


This is based on poking around in the crash dump:
    BUG: unable to handle kernel NULL pointer dereference at 0000000000000060
    IP: [<ffffffff8142bb40>] __netif_receive_skb+0x60/0x6e0
    crash> dis -rl ffffffff8142bb40
    ....
    /usr/src/debug/kernel-2.6.32-220.7.1.el6/linux-2.6.32-220.7.1.el6.x86_64/include/linux/netpoll.h:
86
    0xffffffff8142bb33 <__netif_receive_skb+83>:    mov    0x20(%rbx),%r12
    0xffffffff8142bb37 <__netif_receive_skb+87>:    mov    %r12,-0x38(%rbp)
    0xffffffff8142bb3b <__netif_receive_skb+91>:    lea    0x60(%r12),%rax
    0xffffffff8142bb40 <__netif_receive_skb+96>:    cmp    %rax,0x60(%r12)



I *think* this means that "&skb->dev->napi_list" is null when we're
trying to compare it, rather than being a list.

If it matters, this is inside LXC containers.
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