netdev - Re: kernel BUG in ipmr_queue

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Date:	Fri, 30 Oct 2015 11:36:58 +0100
From:	Florian Westphal <fw@...len.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Ani Sinha <ani@...sta.com>, Florian Westphal <fw@...len.de>,
	netdev@...r.kernel.org, ani@...rban.org, fruggeri@...sta.com
Subject: Re: kernel BUG in ipmr_queue_xmit()

Eric Dumazet <eric.dumazet@...il.com> wrote:
> > Signed-off-by: Ani Sinha <ani@...sta.com>
> > ---
> >  net/ipv4/ipmr.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
> > index 866ee89..48df3cc 100644
> > --- a/net/ipv4/ipmr.c
> > +++ b/net/ipv4/ipmr.c
> > @@ -936,7 +936,9 @@ static void ipmr_cache_resolve(struct net *net, struct mr_table *mrt,
> >  
> >  			rtnl_unicast(skb, net, NETLINK_CB(skb).portid);
> >  		} else {
> > +			preempt_disable();
> >  			ip_mr_forward(net, mrt, skb, c, 0);
> > +			preempt_enable();
> >  		}
> >  	}
> >  }
> 
> I do not believe this fix is correct.

Yes, sorry.  I should have suggested local_bh_disable instead.

> Better replace the
> IP_INC_STATS_BH() by IP_INC_STATS()
>
> and IP_ADD_STATS_BH() by IP_ADD_STATS()

Hmm, whats the rationale for this?

Note that IP_ADD_STATS_BH in question is unconditional (not in
error path).  It seems that its virtually always called from softirq
except in the setsockopt case.

Thanks Eric.
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