netdev - Re: [PATCH 1/7] xfrm: remove policy lock when accessing policy->walk.dead

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Message-ID: <20100330115351.GA5731@gondor.apana.org.au>
Date:	Tue, 30 Mar 2010 19:53:51 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Timo Teräs <timo.teras@....fi>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH 1/7] xfrm: remove policy lock when accessing
	policy->walk.dead

On Tue, Mar 30, 2010 at 07:55:07AM +0300, Timo Teräs wrote:
> Herbert Xu wrote:
>> On Mon, Mar 29, 2010 at 05:12:38PM +0300, Timo Teras wrote:
>>> @@ -1132,7 +1119,7 @@ int xfrm_sk_policy_insert(struct sock *sk, int dir, struct xfrm_policy *pol)
>>>  		__xfrm_policy_link(pol, XFRM_POLICY_MAX+dir);
>>>  	}
>>>  	if (old_pol)
>>> -		__xfrm_policy_unlink(old_pol, XFRM_POLICY_MAX+dir);
>>> +		old_pol = __xfrm_policy_unlink(old_pol, XFRM_POLICY_MAX+dir);
>>>  	write_unlock_bh(&xfrm_policy_lock);
>>>   	if (old_pol) {
>>
>> So when can this actually fail?
>
> Considering that the socket reference is received from the sk->sk_policy,
> and the hash bucket we use is "XFRM_POLICY_MAX+dir", it's non-obvious if
> it can fail or not.
>
> It would look like the timer can kill a policy and unlink it, but it
> would still be found from sk_policy.

Socket policies cannot expire.

In fact, they probably shouldn't even be on the bydst or any other
hash table.  I think the only reason they're there at all is because
the hash table was added to __xfrm_policy_link which happens to be
used by socket policies.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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