netdev - Re: [PATCH 7/9] rhashtable: Per bucket locks & deferred expansion/shrinking

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Message-ID: <20150116155835.GA15052@casper.infradead.org>
Date:	Fri, 16 Jan 2015 15:58:35 +0000
From:	Thomas Graf <tgraf@...g.ch>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	kernel@...r.kernel.org, herbert@...dor.apana.org.au,
	paulmck@...ux.vnet.ibm.com, edumazet@...gle.com,
	john.r.fastabend@...el.com, josh@...htriplett.org,
	netfilter-devel@...r.kernel.org
Subject: Re: [PATCH 7/9] rhashtable: Per bucket locks & deferred
 expansion/shrinking

On 01/16/15 at 03:34pm, Patrick McHardy wrote:
> On 15.12, Thomas Graf wrote:
> > In the event of an expansion or shrinking, the new bucket table allocated
> > is exposed as a so called future table as soon as the resize process
> > starts.  Lookups, deletions, and insertions will briefly use both tables.
> > The future table becomes the main table after an RCU grace period and
> > initial linking of the old to the new table was performed. Optimization
> > of the chains to make use of the new number of buckets follows only the
> > new table is in use.
> 
> AFAICT nft_hash_walk() will miss new entries during this period.
> Am I missing anything here?

A walker may not see insertions that occur after the walker was started
if resizing is enabled. Is that a problem for nftables?
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