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Date:	Tue, 02 Feb 2010 12:07:06 -0500
From:	Jon Masters <>
To:	Patrick McHardy <>
Cc:	Eric Dumazet <>,
	Alexey Dobriyan <>,
	linux-kernel <>,
	netdev <>,
	netfilter-devel <>,
	"Paul E. McKenney" <>
Subject: Re: [PATCH] netfilter: per netns nf_conntrack_cachep

On Tue, 2010-02-02 at 17:48 +0100, Patrick McHardy wrote:
> Jon Masters wrote:
> > On Tue, 2010-02-02 at 06:35 -0500, Jon Masters wrote:
> > 
> >> I think there's something more fundamental going on here.
> > 
> > What happens is the conntrack code attempts to free
> > nf_conntrack_untracked back into the SL[U]B cache from which it
> > allocates other ct's.
> That shouldn't happen, the untracked conntrack is initialized to a
> refcount of 1, which is never released.

Ah, but I think it is :) It's also re-initialized (with an atomic_set)
every time a new namespace is created, whereas this should probably only
be done in the init_init_net code, not in init_net :)

> > There's just one problem...that's a static struct
> > not from the cache. So, this is why we end up with the SLAB being
> > corrupted and the address immediately following the
> > nf_conntrack_untracked being corrupted.
> > 
> > I shoved some debug comments into the destroy code to see if we were
> > trying to free nf_conntrack_untracked, and bingo. I have shoved a panic
> > in there now, will send you a backtrace.
> Thanks.

No problem. And thanks for your help. I'm sorry if I sound frustrated at
this, it's just causing all of my test machines running KVM guests to
fall over :)


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