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

[Rafael J. Wysocki]

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?

> 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
>