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

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Date:	Mon, 07 Oct 2013 16:54:07 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	John Stultz <john.stultz@...aro.org>
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 Mon, 2013-10-07 at 15:52 -0700, John Stultz wrote:
> While enabling lockdep on seqlocks, I ran across the warning below
> caused by the ipv6 stats being updated in both irq and non-irq context.

You mean a lockdep warning on a seqcount in this context, right ?

> 
> This patch changes from IP6_INC_STATS_BH to IP6_INC_STATS (suggested
> by Eric Dumazet) to resolve this problem.
...
> Cc: Eric Dumazet <eric.dumazet@...il.com>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Alexey Kuznetsov <kuznet@....inr.ac.ru>
> Cc: James Morris <jmorris@...ei.org>
> Cc: Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>
> Cc: Patrick McHardy <kaber@...sh.net>
> Signed-off-by: John Stultz <john.stultz@...aro.org>
> ---
>  net/ipv6/ip6_output.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index 3a692d5..7e63c1e 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -909,7 +909,7 @@ static int ip6_dst_lookup_tail(struct sock *sk,
>  
>  out_err_release:
>  	if (err == -ENETUNREACH)
> -		IP6_INC_STATS_BH(net, NULL, IPSTATS_MIB_OUTNOROUTES);
> +		IP6_INC_STATS(net, NULL, IPSTATS_MIB_OUTNOROUTES);
>  	dst_release(*dst);
>  	*dst = NULL;
>  	return err;

This one is certainly a bug fix, David please consider adding it to your
net tree

Bug added in commit ca46f9c834913f ("[IPv6] SNMP: Increment OutNoRoutes
when connecting to unreachable network")

Acked-by: Eric Dumazet <edumazet@...gle.com>



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