linux-kernel - Re: [PATCH -next] power/qos: fix a data race in pm_qos_*

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Date:   Tue, 25 Feb 2020 19:34:18 -0500
From:   Qian Cai <cai@....pw>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Marco Elver <elver@...gle.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] power/qos: fix a data race in pm_qos_*_value



> On Feb 25, 2020, at 7:10 PM, Rafael J. Wysocki <rafael@...nel.org> wrote:
> 
> The target_value field in struct pm_qos_constraints is used for
> lockless access to the effective constraint value of a given QoS list,
> so the readers of it cannot expect it to always reflect the most
> recent effective constraint value.  However, they can and do expect it
> to be equal to a valid effective constraint value computed at a
> certain time in the past (event though it may not be the most recent
> one), so add READ|WRITE_ONCE() annotations around the target_value
> accesses to prevent the compiler from possibly causing that
> expectation to be unmet by generating code in an exceptionally
> convoluted way.

Perfect. I’ll send a v2 for that unless you would like to squash it in.