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Message-ID: <1380223848.3165.207.camel@edumazet-glaptop>
Subject: Re: [PATCH 4/4] [RFC] ipv6: Fix for possible ipv6 seqlock deadlock
From: Eric Dumazet <eric.dumazet@gmail.com>
To: John Stultz <john.stultz@linaro.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.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>
Date: Thu, 26 Sep 2013 12:30:48 -0700
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	 <1380220464-28840-5-git-send-email-john.stultz@linaro.org>
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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)