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

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Message-ID: <20150202094819.GA22611@casper.infradead.org>
Date:	Mon, 2 Feb 2015 09:48:19 +0000
From:	Thomas Graf <tgraf@...g.ch>
To:	Ying Xue <ying.xue@...driver.com>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>, netdev@...r.kernel.org
Subject: Re: rhashtable: Fix potential crash on destroy in rhashtable_shrink

On 02/02/15 at 05:34pm, Ying Xue wrote:
> On 01/31/2015 05:36 PM, 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.
> > 
> 
> Sorry, I cannot understand the scenario.
> 
> When we free the table in rhashtable_destroy(), we call
> cancel_work_sync() to synchronously cancel the work. So, why does your
> described crash still happen?

It's nft_hash specific. nft_hash frees all entries under ht->mutex without
unlinking them upon destroy and sets being_destroyed before doing. Therefore
it must be ensured that a resize is not started afterwards because the table
contains freed entries.
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