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From: Qian Cai <cai@lca.pw>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
	elver@google.com, Linux PM <linux-pm@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH -next] power/qos: fix a data race in pm_qos_*_value
Date: Sun, 23 Feb 2020 20:01:33 -0500	[thread overview]
Message-ID: <62491094-D13B-4EED-8190-4AA4EB77036B@lca.pw> (raw)
In-Reply-To: <CAJZ5v0iSEV9S=zTa9++vUCO6GTfBE2sxNY+b4mMMt4Y6RCRvjA@mail.gmail.com>



> On Feb 23, 2020, at 7:12 PM, Rafael J. Wysocki <rafael@kernel.org> wrote:
> 
> It may be a bug under certain conditions, but you don't mention what
> conditions they are.  Reporting it as a general bug is not accurate at
> the very least.

Could we rule out load tearing, store tearing and reload of global_req in cpuidle_governor_latency() for all compilers and architectures which could introduce logic bugs?

	int global_req = cpu_latency_qos_limit();

	if (device_req > global_req)
		device_req = global_req;

If under register pressure, the compiler might get ride of the tmp variable, i.e.,

If (device_req > cpu_latency_qos_limit())
—-> race with the writer.
         device_req = cpu_latency_qos_limit();



  reply	other threads:[~2020-02-24  1:01 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-21 21:09 Qian Cai
2020-02-24  0:12 ` Rafael J. Wysocki
2020-02-24  1:01   ` Qian Cai [this message]
2020-02-24  9:54     ` Rafael J. Wysocki
2020-02-24 19:02       ` Qian Cai
2020-02-26  0:10         ` Rafael J. Wysocki
2020-02-26  0:34           ` Qian Cai

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