netdev - Re: xfrm_state locking regression...

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Date:	Tue, 23 Sep 2008 21:07:09 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Timo Teräs <timo.teras@....fi>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: xfrm_state locking regression...

On Tue, Sep 23, 2008 at 04:01:29PM +0300, Timo Teräs wrote:
>
> So, what to do?
> 1. Go back to: list_del_rcu, xfrm_state_hold(all.next) on delete and
>    xfrm_state_put(all.next) on destruct.
> 2. Add per-entry hlist of walkers currently referencing it.
> 3. Use the global walker list.
> 
> 1 can keep memory allocated until userland wakes up. 2 & 3 can make
> the delete of that entry slow if there's many walkers suspended.

I'd cross 3 off the list because 2 is just so much better :)

I'd slightly lean towards 2 but now that you mention it yes even
that is vulnerable to loads of dumpers sitting on the same entry.
So SELINUX folks wouldn't like that :)

> Btw. the current stuff in net-next is broken. There's no locking
> for xfrm_state_walkers list handling.

What about xfrm_cfg_mutex?

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