Date: Fri, 23 Nov 2007 22:15:24 +0300
From: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
To: Matt Mackall <mpm@selenic.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
       Simon Arlott <simon@fire.lp0.eu>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       netdev@vger.kernel.org, Ingo Molnar <mingo@redhat.com>
Subject: Re: 2.6.23 WARNING: at kernel/softirq.c:139 local_bh_enable()
Message-ID: <20071123191524.GA6273@2ka.mipt.ru>
References: <4745DCD7.8070805@simon.arlott.org.uk> <20071123002157.cb27f4a1.akpm@linux-foundation.org> <20071123105518.GA22062@2ka.mipt.ru> <20071123170756.GV19691@waste.org> <20071123175757.GA23991@2ka.mipt.ru> <20071123185943.GZ19691@waste.org>
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On Fri, Nov 23, 2007 at 12:59:43PM -0600, Matt Mackall (mpm@selenic.com) wrote:
> So I'd be surprised if that was a problem. But I can imagine having
> problems for skbs without destructors which run into one of these in
> __kfree_skb:
> 
> dst_release
> secpath_put
> nf_conntrack_put
> nf_conntrack_put_reasm
> nf_bridge_put
> 
> ..some or all of which assume a softirq context.

bridging is ok, others require softirq context.
I've sent a patch (the last one should be ok) to guard against xfrm and
connection tracking.

> > No matter if we are under memory pressure or whatever - it is not
> > allowed - a lot of skbs are supposed to be freed in softirq context,
> > that is why dev_kfree_skb_any() exists.
> 
> Some skbs we definitely -can- free in irq context. The only ones we
> care about are the ones generated by netpoll. If there's a reason you
> think netpoll's own skbs can't be freed, please describe it.

Only some and to distinguish them we can not use destructor - if it is
set (even empty function) it will fire an alarm.

> > I think we can drop skbs _without_ destructor from the queue though in
> > that conditions given that we actually need only one.
> 
> Huh?

Don't mind - friday...
I posted a patch (third one should be ok) to fix this issue.

-- 
	Evgeniy Polyakov
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