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From: "Emilio G. Cota" <cota@braap.org>
To: "Alex Bennée" <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
Subject: Re: [Qemu-devel] [RFC 7/8] util/qht: atomically set b->hashes
Date: Mon, 19 Sep 2016 14:06:14 -0400	[thread overview]
Message-ID: <20160919180614.GA8713@flamenco> (raw)
In-Reply-To: <20160919155139.28371-8-alex.bennee@linaro.org>

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

  reply	other threads:[~2016-09-19 18:06 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-19 15:51 [Qemu-devel] [RFC 0/8] A couple of fixes for ThreadSanitizer Alex Bennée
2016-09-19 15:51 ` [Qemu-devel] [RFC 1/8] ui/vnc-enc-tight: add abort() for unexpected default Alex Bennée
2016-09-20  8:02   ` Marc-André Lureau
2016-09-20  8:24     ` Paolo Bonzini
2016-09-20 14:59       ` Alex Bennée
2016-09-19 15:51 ` [Qemu-devel] [RFC 2/8] tcg/optimize: move default return out of if statement Alex Bennée
2016-09-20  8:02   ` Marc-André Lureau
2016-09-19 15:51 ` [Qemu-devel] [RFC 3/8] new: blacklist.tsan Alex Bennée
2016-09-20  8:03   ` Marc-André Lureau
2016-09-19 15:51 ` [Qemu-devel] [RFC 4/8] seqlock: use atomic writes for the sequence Alex Bennée
2016-09-19 15:51 ` [Qemu-devel] [RFC 5/8] qom/object: update class cache atomically Alex Bennée
2016-09-20  8:36   ` Marc-André Lureau
2016-09-20 14:59     ` Alex Bennée
2016-09-20 15:04       ` Paolo Bonzini
2016-09-19 15:51 ` [Qemu-devel] [RFC 6/8] cpu: atomically modify cpu->exit_request Alex Bennée
2016-09-19 15:51 ` [Qemu-devel] [RFC 7/8] util/qht: atomically set b->hashes Alex Bennée
2016-09-19 18:06   ` Emilio G. Cota [this message]
2016-09-19 18:37     ` Paolo Bonzini
2016-09-19 19:06       ` Emilio G. Cota
2016-09-20  7:39         ` Paolo Bonzini
2016-09-22  9:51           ` Alex Bennée
2016-09-19 15:51 ` [Qemu-devel] [RFC 8/8] .travis.yml: add gcc sanitizer build Alex Bennée

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