linux-kernel - Re: [PATCH v4 5/6] media: mt9m114: Fix deadlock in get_frame_interval/set_frame

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Message-ID: <20250423181620.GD2675@pendragon.ideasonboard.com>
Date: Wed, 23 Apr 2025 21:16:20 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Mathis Foerst <mathis.foerst@...com>
Cc: linux-kernel@...r.kernel.org,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	linux-media@...r.kernel.org, devicetree@...r.kernel.org,
	manuel.traut@...com, mathis.foerst@...hlke.com,
	stable@...r.kernel.org
Subject: Re: [PATCH v4 5/6] media: mt9m114: Fix deadlock in
 get_frame_interval/set_frame_interval

Hi Mathis,

Thank you for the patch.

On Fri, Mar 07, 2025 at 10:31:39AM +0100, Mathis Foerst wrote:
> Getting / Setting the frame interval using the V4L2 subdev pad ops
> get_frame_interval/set_frame_interval causes a deadlock, as the
> subdev state is locked in the [1] but also in the driver itself.
> 
> In [2] it's described that the caller is responsible to acquire and
> release the lock in this case. Therefore, acquiring the lock in the
> driver is wrong.
> 
> Remove the lock acquisitions/releases from mt9m114_ifp_get_frame_interval()
> and mt9m114_ifp_set_frame_interval().
> 
> [1] drivers/media/v4l2-core/v4l2-subdev.c - line 1129
> [2] Documentation/driver-api/media/v4l2-subdev.rst
> 
> Fixes: 24d756e914fc ("media: i2c: Add driver for onsemi MT9M114 camera sensor")
> Cc: stable@...r.kernel.org
> 

You can delete this blank line.

> Signed-off-by: Mathis Foerst <mathis.foerst@...com>

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

> ---
>  drivers/media/i2c/mt9m114.c | 8 --------
>  1 file changed, 8 deletions(-)
> 
> diff --git a/drivers/media/i2c/mt9m114.c b/drivers/media/i2c/mt9m114.c
> index 65b9124e464f..79c97ab19be9 100644
> --- a/drivers/media/i2c/mt9m114.c
> +++ b/drivers/media/i2c/mt9m114.c
> @@ -1644,13 +1644,9 @@ static int mt9m114_ifp_get_frame_interval(struct v4l2_subdev *sd,
>  	if (interval->which != V4L2_SUBDEV_FORMAT_ACTIVE)
>  		return -EINVAL;
>  
> -	mutex_lock(sensor->ifp.hdl.lock);
> -
>  	ival->numerator = 1;
>  	ival->denominator = sensor->ifp.frame_rate;
>  
> -	mutex_unlock(sensor->ifp.hdl.lock);
> -
>  	return 0;
>  }
>  
> @@ -1669,8 +1665,6 @@ static int mt9m114_ifp_set_frame_interval(struct v4l2_subdev *sd,
>  	if (interval->which != V4L2_SUBDEV_FORMAT_ACTIVE)
>  		return -EINVAL;
>  
> -	mutex_lock(sensor->ifp.hdl.lock);
> -
>  	if (ival->numerator != 0 && ival->denominator != 0)
>  		sensor->ifp.frame_rate = min_t(unsigned int,
>  					       ival->denominator / ival->numerator,
> @@ -1684,8 +1678,6 @@ static int mt9m114_ifp_set_frame_interval(struct v4l2_subdev *sd,
>  	if (sensor->streaming)
>  		ret = mt9m114_set_frame_rate(sensor);
>  
> -	mutex_unlock(sensor->ifp.hdl.lock);
> -
>  	return ret;
>  }
>  

-- 
Regards,

Laurent Pinchart