netdev - Re: rhashtable: Fix reader/rehash race

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Message-ID: <20150313105435.GA17829@casper.infradead.org>
Date:	Fri, 13 Mar 2015 10:54:35 +0000
From:	Thomas Graf <tgraf@...g.ch>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	netdev@...r.kernel.org
Subject: Re: rhashtable: Fix reader/rehash race

On 03/13/15 at 09:36pm, Herbert Xu wrote:
> rhashtable_remove is fine because the rehasher has to take the
> same lock to move things over.  That's what guarantees the new
> future_tbl to be visible if it moved the to-be-removed object
> over to the new table.
> 
> IOW if rhashtable_remove couldn't see the future_tbl then that
> can only mean that the rehasher has yet to take the lock on that
> bucket which implies that the object if it existed at all is still
> in that bucket.

Ah, it works because the future_tbl load can't be reordered in
front of the acquire. Thanks for the explanation.
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