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Message-ID: <5245AB9B.6040606@linaro.org>
Date: Fri, 27 Sep 2013 09:00:27 -0700
From: John Stultz <john.stultz@linaro.org>
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To: Ingo Molnar <mingo@kernel.org>
CC: Eric Dumazet <eric.dumazet@gmail.com>, LKML <linux-kernel@vger.kernel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        "David S. Miller" <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        James Morris <jmorris@namei.org>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Patrick McHardy <kaber@trash.net>
Subject: Re: [PATCH 4/4] [RFC] ipv6: Fix for possible ipv6 seqlock deadlock
References: <1380220464-28840-1-git-send-email-john.stultz@linaro.org> <1380220464-28840-5-git-send-email-john.stultz@linaro.org> <1380223848.3165.207.camel@edumazet-glaptop> <52448F0F.9050408@linaro.org> <20130927054712.GB6597@gmail.com>
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On 09/26/2013 10:47 PM, Ingo Molnar wrote:
> * John Stultz <john.stultz@linaro.org> wrote:
>
>> On 09/26/2013 12:30 PM, Eric Dumazet wrote:
>>> On Thu, 2013-09-26 at 11:34 -0700, John Stultz wrote:
>>>> While enabling lockdep on seqlocks, I ran accross the warning below
>>>> caused by the ipv6 stats being updated in both irq and non-irq context.
>>>>
>>>> This is a novice attempt to correct the issue, and with this patch
>>>> the warning goes away. Any better solutions would be appreciated!
>>> ...
>>>
>>>>  
>>>>  out_err_release:
>>>> -	if (err == -ENETUNREACH)
>>>> +	if (err == -ENETUNREACH) {
>>>> +		unsigned long flags;
>>>> +		/* some of the stats are locked in irq context */
>>>> +		local_irq_save(flags);
>>>>  		IP6_INC_STATS_BH(net, NULL, IPSTATS_MIB_OUTNOROUTES);
>>>> +		local_irq_restore(flags);
>>>> +	}
>>>>  	dst_release(*dst);
>>>>  	*dst = NULL;
>>>>  	return err;
>>> You better change IP6_INC_STATS_BH() to IP6_INC_STATS()
>>>
>>> On x86 for example, no extra code will be generated (no need to disable
>>> hard or soft irqs)
>> Ah, thanks! Verified it resolves the warning as well, so I've changed my
>> patch to use your suggestion.
> Btw., is this a deadlock that could occur upstream? If yes then adding a 
> Cc: <stable@kernel.org> tag might be warranted.

It seems as such, so I'll add stable on my next submission.

thanks
-john