linux-kernel - Re: [PATCH 01/10] drm/connector: add mutex to protect ELD from concurrent access

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Message-ID: <87r06q5qou.fsf@intel.com>
Date: Mon, 02 Dec 2024 12:23:29 +0200
From: Jani Nikula <jani.nikula@...ux.intel.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>, Maarten Lankhorst
 <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>,
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>,
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Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 amd-gfx@...ts.freedesktop.org, linux-arm-kernel@...ts.infradead.org,
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 freedreno@...ts.freedesktop.org
Subject: Re: [PATCH 01/10] drm/connector: add mutex to protect ELD from
 concurrent access

On Sun, 01 Dec 2024, Dmitry Baryshkov <dmitry.baryshkov@...aro.org> wrote:
> The connector->eld is accessed by the .get_eld() callback. This access
> can collide with the drm_edid_to_eld() updating the data at the same
> time. Add drm_connector.eld_mutex to protect the data from concurrenct
> access. Individual drivers are not updated (to reduce possible issues
> while applying the patch), maintainers are to find a best suitable way
> to lock that mutex while accessing the ELD data.

Missed clear_eld().

BR,
Jani.

>
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> ---
>  drivers/gpu/drm/drm_connector.c | 1 +
>  drivers/gpu/drm/drm_edid.c      | 4 ++++
>  include/drm/drm_connector.h     | 5 ++++-
>  3 files changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index fc35f47e2849ed6786d6223ac9c69e1c359fc648..bbdaaf7022b62d84594a29f1b60144920903a99a 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -277,6 +277,7 @@ static int __drm_connector_init(struct drm_device *dev,
>  	INIT_LIST_HEAD(&connector->probed_modes);
>  	INIT_LIST_HEAD(&connector->modes);
>  	mutex_init(&connector->mutex);
> +	mutex_init(&connector->eld_mutex);
>  	mutex_init(&connector->edid_override_mutex);
>  	mutex_init(&connector->hdmi.infoframes.lock);
>  	connector->edid_blob_ptr = NULL;
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 855beafb76ffbecf5c08d58e2f54bfb76f30b930..f0ca77bd42fd518d505d0db78557e0c8d83efb29 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -5657,6 +5657,8 @@ static void drm_edid_to_eld(struct drm_connector *connector,
>  	if (!drm_edid)
>  		return;
>  
> +	mutex_lock(&connector->eld_mutex);
> +
>  	mnl = get_monitor_name(drm_edid, &eld[DRM_ELD_MONITOR_NAME_STRING]);
>  	drm_dbg_kms(connector->dev, "[CONNECTOR:%d:%s] ELD monitor %s\n",
>  		    connector->base.id, connector->name,
> @@ -5717,6 +5719,8 @@ static void drm_edid_to_eld(struct drm_connector *connector,
>  	drm_dbg_kms(connector->dev, "[CONNECTOR:%d:%s] ELD size %d, SAD count %d\n",
>  		    connector->base.id, connector->name,
>  		    drm_eld_size(eld), total_sad_count);
> +
> +	mutex_unlock(&connector->eld_mutex);
>  }
>  
>  static int _drm_edid_to_sad(const struct drm_edid *drm_edid,
> diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
> index e3fa43291f449d70f3b92a00985336c4f2237bc6..1e2b25e204cb523d61d30f5409faa059bf2b86eb 100644
> --- a/include/drm/drm_connector.h
> +++ b/include/drm/drm_connector.h
> @@ -2001,8 +2001,11 @@ struct drm_connector {
>  	struct drm_encoder *encoder;
>  
>  #define MAX_ELD_BYTES	128
> -	/** @eld: EDID-like data, if present */
> +	/** @eld: EDID-like data, if present, protected by @eld_mutex */
>  	uint8_t eld[MAX_ELD_BYTES];
> +	/** @eld_mutex: protection for concurrenct access to @eld */
> +	struct mutex eld_mutex;
> +
>  	/** @latency_present: AV delay info from ELD, if found */
>  	bool latency_present[2];
>  	/**

-- 
Jani Nikula, Intel