linux-kernel - Re: [PATCH] PM: add: move warn message out of mutex lock.

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Message-ID: <408f4579.bfd0.191b8ac0e66.Coremail.00107082@163.com>
Date: Wed, 4 Sep 2024 00:16:09 +0800 (CST)
From: "David Wang" <00107082@....com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: len.brown@...el.com, pavel@....cz, gregkh@...uxfoundation.org, 
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PM: add: move warn message out of mutex lock.

Hi,

At 2024-09-03 22:10:16, "Rafael J. Wysocki" <rafael@...nel.org> wrote:
>On Tue, Sep 3, 2024 at 3:01 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>>
>> On Mon, Sep 2, 2024 at 7:50 AM David Wang <00107082@....com> wrote:
>> >
>> > dpm_list_mtx does not protect any data used by
>> > dev_warn for checking parent's power, move
>> > dev_warn out of mutex lock block make the
>> > lock more efficient, especially when the warn
>> > is triggered.
>>
>> It does protect the power.is_prepared flag of the parent.
>
>In fact, the update of it in device_resume() is racy with respect to
>the check in device_pm_add(), but the purpose of it is mostly to allow
>the device driver's resume callback to add children without triggering
>the warning.


Kind of confused by this... if dpm_list_mtx could protect power.is_prepared, 
then codes that change power.is_prepared should also hold this lock, but normally
they only use device_lock(dev);


David