linux-kernel - Re: [PATCH 4/8] rhashtable: fix race in nested_table

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Message-ID: <20180506051859.w7evarps5jdcplz6@gondor.apana.org.au>
Date:   Sun, 6 May 2018 13:18:59 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     NeilBrown <neilb@...e.com>
Cc:     Thomas Graf <tgraf@...g.ch>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/8] rhashtable: fix race in nested_table_alloc()

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@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt