netdev - Re: [net PATCH] netfilter: only warn once on wrong seqadj usage

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Date:	Mon, 6 Jan 2014 08:32:39 +0100
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	Jesper Dangaard Brouer <brouer@...hat.com>,
	Pablo Neira Ayuso <pablo@...filter.org>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	netfilter-devel@...r.kernel.org, Florian Westphal <fw@...len.de>,
	Daniel Borkmann <dborkman@...hat.com>,
	Flavio Leitner <fbl@...hat.com>,
	"lvs-devel@...r.kernel.org" <lvs-devel@...r.kernel.org>
Subject: Re: [net PATCH] netfilter: only warn once on wrong seqadj usage

On Sat, 4 Jan 2014 13:16:48 +0000
Patrick McHardy <kaber@...sh.net> wrote:

> On Sat, Jan 04, 2014 at 02:10:43PM +0100, Jesper Dangaard Brouer wrote:
> > Avoid potentially spamming the kernel log with WARN splash messages
> > when catching wrong usage of seqadj, by simply using WARN_ONCE.
> > 
> > This is a followup to commit db12cf274353 (netfilter: WARN about
> > wrong usage of sequence number adjustments)
> > 
> > Suggested-by: Flavio Leitner <fbl@...hat.com>
> > Suggested-by: Daniel Borkmann <dborkman@...hat.com>
> > Suggested-by: Florian Westphal <fw@...len.de>
> > Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
> > ---
> > Nitpick found by internal RedHat review process ;-)
> > 
> >  net/netfilter/nf_conntrack_seqadj.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> > 
> > diff --git a/net/netfilter/nf_conntrack_seqadj.c b/net/netfilter/nf_conntrack_seqadj.c
> > index b2d38da..f6e2ae9 100644
> > --- a/net/netfilter/nf_conntrack_seqadj.c
> > +++ b/net/netfilter/nf_conntrack_seqadj.c
> > @@ -37,7 +37,7 @@ int nf_ct_seqadj_set(struct nf_conn *ct, enum ip_conntrack_info ctinfo,
> >  		return 0;
> >  
> >  	if (unlikely(!seqadj)) {
> > -		WARN(1, "Wrong seqadj usage, missing nfct_seqadj_ext_add()\n");
> > +		WARN_ONCE(1, "Missing nfct_seqadj_ext_add() setup call\n");
> >  		return 0;
> 
> I missed the patch that added the WARN. Since when do we add runtime checks
> for API misuse instead of simply letting it crash?

We changed an existing API which broke IPVS. And I think we still have
a use-case in IPVS, which can hit this case/bug, thus I added a stack
dump warning (instead of crashing), so I can catch this use-case and
fix it later.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Sr. Network Kernel Developer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer
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