netdev - Re: kernel BUG in ipmr_queue

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Message-ID: <20151030001510.GG18062@breakpoint.cc>
Date:	Fri, 30 Oct 2015 01:15:10 +0100
From:	Florian Westphal <fw@...len.de>
To:	Ani Sinha <ani@...sta.com>
Cc:	netdev@...r.kernel.org, ani@...rban.org, fruggeri@...sta.com
Subject: Re: kernel BUG in ipmr_queue_xmit()

Ani Sinha <ani@...sta.com> wrote:

[ trimmed CC list ]

> We are noticing the following kernel BUG in 3.18 kernel. The 
> code path that leads to the crash is the following :
> 
>  ip_mroute_setsockopt()
>   ->ipmr_mfc_add()
>       ->ipmr_cache_resolve()
>         ->ip_mr_forward()
>            -> ipmr_queue_xmit()
>              -> ipmr_forward_finish()
>                ->IP_INC_STATS_BH()
>                   -> SNMP_INC_STATS64_BH()
>                     -> SNMP_INC_STATS_BH()
>                           -> __this_cpu_inc()
>                               -> __this_cpu_add()
>                                   -> __this_cpu_preempt_check()
>                                      -> check_preemption_disabled()
> 
> I have verified that preempt_count() is 0 when the crash happens.
> Is anyone else seeing the same crash in the laetst upstream code? I dug 
> around a little bit and it does not look like there were any fixes that 
> went into post 3.18 kernel which could have disabled preemption in this 
> code path but I could be wrong. 
> 
> thoughts?

Send a patch to preempt_disable before ip_mr_forward call in the affected
setsockopt path?
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