netdev - Re: rhashtable: Fix potential crash on destroy in rhashtable

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Message-ID: <20150131112209.GA29869@gondor.apana.org.au>
Date:	Sat, 31 Jan 2015 22:22:09 +1100
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Thomas Graf <tgraf@...g.ch>
Cc:	netdev@...r.kernel.org
Subject: Re: rhashtable: Fix potential crash on destroy in rhashtable_shrink

On Sat, Jan 31, 2015 at 11:16:52AM +0000, Thomas Graf wrote:
> On 01/31/15 at 08:36pm, Herbert Xu wrote:
> > The current being_destroyed check in rhashtable_expand is not
> > enough since if we start a shrinking process after freeing all
> > elements in the table that's also going to crash.
> 
> (The check in expand() is just an optimization to drop out of
>  work cycles if it does not make sense to continue anymore.)
> 
> > 
> > This patch adds a being_destroyed check to the deferred worker
> > thread so that we bail out as soon as we take the lock.
> 
> Shouldn't the cancel_work_sync() in rhashtable_destroy() block
> until the deferred worker is done and cancelled?

That's too late.  nft_hash will have freed all the elements
before rhashtable_destroy gets called.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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