linux-kernel - Re: [PATCH 4/4] [RFC] ipv6: Fix for possible ipv6 seqlock deadlock

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Date:	Thu, 26 Sep 2013 12:46:23 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH 4/4] [RFC] ipv6: Fix for possible ipv6 seqlock deadlock

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.

thanks again
-john
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