linux-kernel - Re: [PATCH] inet: further fixes of possible seqlock deadlocks

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Date:	Thu, 28 Nov 2013 23:19:26 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>, jongman.heo@...sung.com,
	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] inet: further fixes of possible seqlock deadlocks

On Thu, Nov 28, 2013 at 10:27:00PM +0100, Hannes Frederic Sowa wrote:
> > > @@ -1524,8 +1524,8 @@ int ip6_push_pending_frames(struct sock *sk)
> > >  	if (proto == IPPROTO_ICMPV6) {
> > >  		struct inet6_dev *idev = ip6_dst_idev(skb_dst(skb));
> > >  
> > > -		ICMP6MSGOUT_INC_STATS_BH(net, idev, icmp6_hdr(skb)->icmp6_type);
> > > -		ICMP6_INC_STATS_BH(net, idev, ICMP6_MIB_OUTMSGS);
> > > +		ICMP6MSGOUT_INC_STATS(net, idev, icmp6_hdr(skb)->icmp6_type);
> > > +		ICMP6_INC_STATS(net, idev, ICMP6_MIB_OUTMSGS);
> > 
> > I am not sure we use a seqlock for ICMP stats.
> > 
> > seqlocks were used for 64bit IP stats
> 
> True, atomic longs get used here in both cases.

I don't really understand why we distinguish between _BH and plain ICMP stat
calls then.

The non-_BH versions deactivate interrupts when updating the per-cpu counter.

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