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

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Message-ID: <CAJZ5v0gEmFj5Yrm0OZx5XhvGStHXx1OsPXGQqmbFQpeYSADkwA@mail.gmail.com>
Date:   Mon, 13 Mar 2023 13:31:11 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Rob Clark <robdclark@...il.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        Rob Clark <robdclark@...omium.org>,
        "Rafael J. Wysocki" <rafael@...nel.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 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?

> 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
>