linux-kernel - Re: [PATCH v2] lib: fix data race in rhashtable_rehash

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Message-ID: <20150922091738.GD13047@pox.localdomain>
Date:	Tue, 22 Sep 2015 11:17:38 +0200
From:	Thomas Graf <tgraf@...g.ch>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	eric.dumazet@...il.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, kcc@...gle.com,
	andreyknvl@...gle.com, glider@...gle.com, ktsan@...glegroups.com,
	paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH v2] lib: fix data race in rhashtable_rehash_one

On 09/22/15 at 10:51am, Dmitry Vyukov wrote:
> rhashtable_rehash_one() uses complex logic to update entry->next field,
> after INIT_RHT_NULLS_HEAD and NULLS_MARKER expansion:
> 
> entry->next = 1 | ((base + off) << 1)
> 
> This can be compiled along the lines of:
> 
> entry->next = base + off
> entry->next <<= 1
> entry->next |= 1
> 
> Which will break concurrent readers.
> 
> NULLS value recomputation is not needed here, so just remove
> the complex logic.
> 
> The data race was found with KernelThreadSanitizer (KTSAN).
> 
> Signed-off-by: Dmitry Vyukov <dvyukov@...gle.com>

Acked-by: Thomas Graf <tgraf@...g.ch>
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