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From:   Qian Cai <cai@lca.pw>
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Subject: Re: [PATCH -next] power/qos: fix a data race in pm_qos_*_value
Date:   Tue, 25 Feb 2020 19:34:18 -0500
Message-Id: <705D8B35-FBB5-4D32-AE63-DD4E773CEC1E@lca.pw>
References: <CAJZ5v0jDjK63R4kbBb_aU7ZBXbCG_vfOW33aVBRbYV7hEOWYqA@mail.gmail.com>
Cc:     "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Marco Elver <elver@google.com>,
        Linux PM <linux-pm@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
In-Reply-To: <CAJZ5v0jDjK63R4kbBb_aU7ZBXbCG_vfOW33aVBRbYV7hEOWYqA@mail.gmail.com>
To:     "Rafael J. Wysocki" <rafael@kernel.org>
Sender: linux-kernel-owner@vger.kernel.org
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> On Feb 25, 2020, at 7:10 PM, Rafael J. Wysocki <rafael@kernel.org> wrote:
>=20
> 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=E2=80=99ll send a v2 for that unless you would like to squash it i=
n.=