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

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Message-ID: <CAJZ5v0gFnHX982G96aU51tirmdQPiQAYExS5CFcjQc4vgXHAtQ@mail.gmail.com>
Date: Tue, 3 Sep 2024 18:23:57 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: David Wang <00107082@....com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, 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.

On Tue, Sep 3, 2024 at 6:16 PM David Wang <00107082@....com> wrote:
>
> 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);

It is confusing, sorry about that.

The bottom line though is that you want to get rid of the spurious
warning in device_pm_add() AFAICS.

To that end, can you please try the patch I sent in the other thread:

https://lore.kernel.org/linux-pm/CAJZ5v0hMnnDjKJLMgcT_p1nnejyyAyaqaA_AF5t+_=PsSMfceQ@mail.gmail.com/