netdev - Re: [PATCH 1/2] xfrm: Force a dst refcount before entering the xfrm type handlers

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Message-Id: <20110316.104118.71120514.davem@davemloft.net>
Date:	Wed, 16 Mar 2011 10:41:18 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	steffen.klassert@...unet.com
Cc:	eric.dumazet@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] xfrm: Force a dst refcount before entering the
 xfrm type handlers

From: Steffen Klassert <steffen.klassert@...unet.com>
Date: Wed, 16 Mar 2011 08:43:06 +0100

> On Wed, Mar 16, 2011 at 12:17:32AM -0700, David Miller wrote:
>> 
>> Steffen we really need to find another way to fix these problems.
>> 
>> We already make way too many expensive atomic operations in these code
>> paths modified by your 3 patches, we should strive to not add new
>> ones.
>> 
> 
> I know that it is exspensive, but we have to take a refcount if
> the crypto layer returns asyncronous. Unfortunately it is too
> late to take the refcount when the crypto layer notifies us about
> that as the skb might be already gone.

We can pass around an atomic_t for the crypto layer to bump when
it decides to take an async path, bump it on entry and upon event
wakeup decrement it.

Actually, a plain atomic_t is a bad idea because we might have to
release the object.  So callbacks with private void pointer arg is
better.
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