Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Sun, 6 May 2018 13:18:59 +0800
From:   Herbert Xu <herbert@gondor.apana.org.au>
To:     NeilBrown <neilb@suse.com>
Cc:     Thomas Graf <tgraf@suug.ch>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/8] rhashtable: fix race in nested_table_alloc()
Message-ID: <20180506051859.w7evarps5jdcplz6@gondor.apana.org.au>
References: <152540595840.18473.11298241115621799037.stgit@noble>
 <152540605432.18473.11813271279255176724.stgit@noble>
 <20180505092907.2qa3scf6bzvubmtt@gondor.apana.org.au>
 <871sepepuj.fsf@notabene.neil.brown.name>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <871sepepuj.fsf@notabene.neil.brown.name>
User-Agent: NeoMutt/20170113 (1.7.2)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Sun, May 06, 2018 at 07:48:20AM +1000, NeilBrown wrote:
>
> The spinlock protects 2 or more buckets.  The nested table contains at
> least 512 buckets, maybe more.
> It is quite possible for two insertions into 2 different buckets to both
> get their spinlock and both try to instantiate the same nested table.

I think you missed the fact that when we use nested tables the spin
lock table is limited to just a single page and hence corresponds
to the first level in the nested table.  Therefore it's always safe.

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