linux-kernel - Re: [PATCH v2 2/2] drm/panthor: Fix OPP refcnt leaks in devfreq initialisation

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Message-ID: <20241003165825.178bb096@collabora.com>
Date: Thu, 3 Oct 2024 16:58:25 +0200
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Adrián Larumbe <adrian.larumbe@...labora.com>,
 kernel@...labora.com
Cc: Rob Herring <robh@...nel.org>, Steven Price <steven.price@....com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
 <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David Airlie
 <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, AngeloGioacchino Del
 Regno <angelogioacchino.delregno@...labora.com>, Liviu Dudau
 <liviu.dudau@....com>, Clément Péron
 <peron.clem@...il.com>, Heiko Stuebner <heiko@...ech.de>, Grant Likely
 <grant.likely@...aro.org>, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] drm/panthor: Fix OPP refcnt leaks in devfreq
 initialisation

On Thu,  3 Oct 2024 14:30:29 +0100
Adrián Larumbe <adrian.larumbe@...labora.com> wrote:

> Make sure in case of errors between the first fetch of an OPP in
> panthor_devfreq_init and its successive put, the error path decrements its
> reference count to avoid OPP object leaks when removing the device.
> 
> Signed-off-by: Adrián Larumbe <adrian.larumbe@...labora.com>
> Fixes: fac9b22df4b1 ("drm/panthor: Add the devfreq logical block")
> ---
>  drivers/gpu/drm/panthor/panthor_devfreq.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_devfreq.c b/drivers/gpu/drm/panthor/panthor_devfreq.c
> index 9d0f891b9b53..ce0ac4563f65 100644
> --- a/drivers/gpu/drm/panthor/panthor_devfreq.c
> +++ b/drivers/gpu/drm/panthor/panthor_devfreq.c
> @@ -197,7 +197,7 @@ int panthor_devfreq_init(struct panthor_device *ptdev)
>  	if (ret && ret != -ENODEV) {
>  		if (ret != -EPROBE_DEFER)
>  			DRM_DEV_ERROR(dev, "Couldn't retrieve/enable sram supply\n");
> -		return ret;
> +		goto opp_err;
>  	}
>  
>  	/*
> @@ -207,7 +207,7 @@ int panthor_devfreq_init(struct panthor_device *ptdev)
>  	ret = dev_pm_opp_set_opp(dev, opp);
>  	if (ret) {
>  		DRM_DEV_ERROR(dev, "Couldn't set recommended OPP\n");
> -		return ret;
> +		goto opp_err;
>  	}
>  
>  	dev_pm_opp_put(opp);
> @@ -242,6 +242,10 @@ int panthor_devfreq_init(struct panthor_device *ptdev)
>  		DRM_DEV_INFO(dev, "Failed to register cooling device\n");
>  
>  	return 0;
> +
> +opp_err:
> +	dev_pm_opp_put(opp);
> +	return ret;

If you re-order things (see the following diff), you shouldn't need
this error path.

--->8---

diff --git a/drivers/gpu/drm/panthor/panthor_devfreq.c b/drivers/gpu/drm/panthor/panthor_devfreq.c
index 9d0f891b9b53..4f1a30f29c06 100644
--- a/drivers/gpu/drm/panthor/panthor_devfreq.c
+++ b/drivers/gpu/drm/panthor/panthor_devfreq.c
@@ -163,13 +163,6 @@ int panthor_devfreq_init(struct panthor_device *ptdev)
 
        cur_freq = clk_get_rate(ptdev->clks.core);
 
-       opp = devfreq_recommended_opp(dev, &cur_freq, 0);
-       if (IS_ERR(opp))
-               return PTR_ERR(opp);
-
-       panthor_devfreq_profile.initial_freq = cur_freq;
-       ptdev->current_frequency = cur_freq;
-
        /* Regulator coupling only takes care of synchronizing/balancing voltage
         * updates, but the coupled regulator needs to be enabled manually.
         *
@@ -200,17 +193,24 @@ int panthor_devfreq_init(struct panthor_device *ptdev)
                return ret;
        }
 
+       opp = devfreq_recommended_opp(dev, &cur_freq, 0);
+       if (IS_ERR(opp))
+               return PTR_ERR(opp);
+
+       panthor_devfreq_profile.initial_freq = cur_freq;
+       ptdev->current_frequency = cur_freq;
+
        /*
         * Set the recommend OPP this will enable and configure the regulator
         * if any and will avoid a switch off by regulator_late_cleanup()
         */
        ret = dev_pm_opp_set_opp(dev, opp);
+       dev_pm_opp_put(opp);
        if (ret) {
                DRM_DEV_ERROR(dev, "Couldn't set recommended OPP\n");
                return ret;
        }
 
-       dev_pm_opp_put(opp);
 
        /* Find the fastest defined rate  */
        opp = dev_pm_opp_find_freq_floor(dev, &freq);