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Date: Mon, 19 Sep 2016 14:06:14 -0400
From: "Emilio G. Cota" <cota@braap.org>
Message-ID: <20160919180614.GA8713@flamenco>
References: <20160919155139.28371-1-alex.bennee@linaro.org>
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Subject: Re: [Qemu-devel] [RFC 7/8] util/qht: atomically set b->hashes
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To: Alex =?iso-8859-1?Q?Benn=E9e?= <alex.bennee@linaro.org>
Cc: qemu-devel@nongnu.org, pbonzini@redhat.com, stefanha@redhat.com, kwolf@redhat.com, mttcg@listserver.greensocs.com, fred.konrad@greensocs.com, a.rigo@virtualopensystems.com, bobby.prani@gmail.com, nikunj@linux.vnet.ibm.com, mark.burton@greensocs.com, jan.kiszka@siemens.com, serge.fdrv@gmail.com, rth@twiddle.net, peter.maydell@linaro.org, claudio.fontana@huawei.com

On Mon, Sep 19, 2016 at 16:51:38 +0100, Alex Bennée wrote:
> ThreadSanitizer detects a possible race between reading/writing the
> hashes. As ordering semantics are already documented for qht we just
> need to ensure a race can't tear the hash value so we can use the
> relaxed atomic_set/read functions.

This was discussed here:

https://lists.gnu.org/archive/html/qemu-devel/2016-05/msg03658.html

To reiterate: reading torn hash values is fine, since the retry will
happen regardless (and all pointers[] remain valid through the RCU
read-critical section).

Couldn't we just tell tsan to ignore it?

Thanks,

		Emilio