Re: [PATCH] [RFC] netfilter: nf_conntrack: don't relase a conntrackwith non-zero refcnt

From: Eric Dumazet
Date: Mon Feb 03 2014 - 11:22:19 EST

On Mon, 2014-02-03 at 00:30 +0100, Pablo Neira Ayuso wrote:
> */
> smp_wmb();
> - atomic_set(&ct->ct_general.use, 1);
> + atomic_set(&ct->ct_general.use, 0);
> return ct;

Hi Pablo !

I think your patch is the way to go, but might need some extra care
with memory barriers.

I believe the smp_wmb() here is no longer needed.

If its a newly allocated memory, no other users can access to ct,
if its a recycled ct, content is already 0 anyway.

After your patch, nf_conntrack_get(&tmpl->ct_general) should increment
an already non zero refcnt, so no memory barrier is needed.

But one smp_wmb() is needed right before this point :

/* The caller holds a reference to this object */
atomic_set(&ct->ct_general.use, 2);

Thanks !

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