linux-kernel - Re: [PATCH 10/13] PM / QoS: Teach lockdep about dev_pm_qos

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Date:   Mon, 13 Mar 2023 07:46:53 -0700
From:   Rob Clark <robdclark@...il.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        Rob Clark <robdclark@...omium.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list:SUSPEND TO RAM" <linux-pm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 10/13] PM / QoS: Teach lockdep about dev_pm_qos_mtx
 locking order

On Mon, Mar 13, 2023 at 5:31 AM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Sun, Mar 12, 2023 at 9:42 PM Rob Clark <robdclark@...il.com> wrote:
> >
> > From: Rob Clark <robdclark@...omium.org>
> >
> > Annotate dev_pm_qos_mtx to teach lockdep to scream about allocations
> > that could trigger reclaim under dev_pm_qos_mtx.
>
> So why is this needed?

Because it allows lockdep to warn about problems even if it hasn't
seen recursion into shrinker yet.

BR,
-R

> > Signed-off-by: Rob Clark <robdclark@...omium.org>
> > ---
> >  drivers/base/power/qos.c | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> >
> > diff --git a/drivers/base/power/qos.c b/drivers/base/power/qos.c
> > index 9cba334b3729..d4addda3944a 100644
> > --- a/drivers/base/power/qos.c
> > +++ b/drivers/base/power/qos.c
> > @@ -1012,3 +1012,14 @@ void dev_pm_qos_hide_latency_tolerance(struct device *dev)
> >         pm_runtime_put(dev);
> >  }
> >  EXPORT_SYMBOL_GPL(dev_pm_qos_hide_latency_tolerance);
> > +
> > +static int __init dev_pm_qos_init(void)
> > +{
> > +       /* Teach lockdep about lock ordering wrt. shrinker: */
> > +       fs_reclaim_acquire(GFP_KERNEL);
> > +       might_lock(&dev_pm_qos_mtx);
> > +       fs_reclaim_release(GFP_KERNEL);
> > +
> > +       return 0;
> > +}
> > +early_initcall(dev_pm_qos_init);
> > --
> > 2.39.2
> >