netdev - Re: xfrm_state locking regression...

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Date:	Wed, 03 Sep 2008 15:01:11 +1000
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	davem@...emloft.net (David Miller)
Cc:	netdev@...r.kernel.org, timo.teras@....fi
Subject: Re: xfrm_state locking regression...

David Miller <davem@...emloft.net> wrote:
>
> This is what added the xfrm_state_lock grabbing in __xfrm_state_destroy().

This is simply bogus.  We should remove the entry from the list
when the state is deleted, not when it's destroyed.  That is, we
should be deleting x->all in places like __xfrm_state_delete instead
of __xfrm_state_destroy.

The fact that we're adding x->all in __xfrm_state_insert means
that we should be deleting it from its counter-part, which is
__xfrm_state_delete.

The same thing applies to the policies of course.  Once a policy
or state is deleted there is no reason why it should show up in a
walk just because some dst is holding onto it.

> ipsec: Fix deadlock in xfrm_state management.
> 
> Ever since commit 4c563f7669c10a12354b72b518c2287ffc6ebfb3
> ("[XFRM]: Speed up xfrm_policy and xfrm_state walking") it is
> illegal to call __xfrm_state_destroy (and thus xfrm_state_put())
> with xfrm_state_lock held.  If we do, we'll deadlock since we
> have the lock already and __xfrm_state_destroy() tries to take
> it again.
> 
> Fix this by pushing the xfrm_state_put() calls after the lock
> is dropped.
> 
> Signed-off-by: David S. Miller <davem@...emloft.net>

However, moving things out of critical sections is always a good
idea.  So I think your patch is an improvement regardless of why
it came about :)

Thanks,
-- 
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Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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