netdev - Re: [PATCH 1/4] flow: virtualize flow cache entry methods

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Date:	Sun, 04 Apr 2010 09:07:12 +0300
From:	Timo Teräs <timo.teras@....fi>
To:	Herbert Xu <herbert@...dor.apana.org.au>
CC:	netdev@...r.kernel.org
Subject: Re: [PATCH 1/4] flow: virtualize flow cache entry methods

Herbert Xu wrote:
> On Sun, Apr 04, 2010 at 08:50:41AM +0300, Timo Teräs wrote:
>> For the common case:
>>
>> 1. Policy deleted; policy->walk.dead set, policy->genid incremented
>> 2. NETDEV_DOWN hook called, calls flow_cache_flush()
>> 3. flow_cache_flush enumerates all policy and bundle refs
>>   in it's cache
>> 4. for each bundle xfrm_bundle_check_fce() is called, which
>>   calls stale_bundle()
>> 5. all bundles using stale policy, fail that check because
>>     xdst->policy_genid != xdst->pols[0]->genid
>>   (checked in xfrm_bundle_ok)
>> 6. flow cache calls entry's ->delete which is dst_free for bundles
>> 7. flow_cache_flush() returns
> 
> Ah, you're doing it in 2/4.  Can we please have each patch be
> a self-contained unit? It should be possible to apply 1/4 and
> have a resulting kernel that works properly without having to
> apply the rest of your patches.

With 1/4 only, the bundle deletion is not touched. In that case
the policy GC deletes explicitly the bundles. The bundles get
deleted immediately, and only the struct xfrm_policy might get
held up allocated longer.

The code flow would be:
 1. xfrm_policy_kill() queues to GC
 2. xfrm_policy_gc_kill() called from xfrm_policy_gc_task()
    frees all bundles in that policy
 3. xfrm_policy_gc_kill() releases it's reference
 4. ... time passes (flush, randomization, or flow hit occurs)
 5. flow cache releases it's final reference, calls
    xfrm_policy_destroy() which only frees the xfrm_policy memory
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