netdev - Re: rhashtable: Fix reader/rehash race

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Message-ID: <20150313103259.GC11089@casper.infradead.org>
Date:	Fri, 13 Mar 2015 10:32:59 +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 08:49am, Herbert Xu wrote:
> It doesn't matter.  The wmb/smb guarauntees that if the reader
> cannot find the element in the old table then it must see the
> new table pointer.  Vice versa if it cannot see the new table
> pointer then the element (if it existed at all) must be in the
> old table.

I understand what you are doing now. I was still thinking
of entries being on both lists in parallel.

One last question though. What about rhashtable_remove()?
The spin_unlock_bh() in __rhashtable_remove() only guarantees
for loads before the release to be completed. The future_tbl
load could still be reordered before the traversal is complete.
I think it needs an smp_rmb() as well.
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