Re: [PATCH 10/13] PM / QoS: Teach lockdep about dev_pm_qos_mtx locking order

[Rob Clark]

On Mon, Mar 13, 2023 at 5:31 AM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
>
> On Sun, Mar 12, 2023 at 9:42 PM Rob Clark <robdclark@xxxxxxxxx> wrote:
> >
> > From: Rob Clark <robdclark@xxxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxxx>
> > ---
> >  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
> >