linux-kernel - Re: [PATCH drm-misc-next 2/3] drm/vc4: plane: protect device resources after removal

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Date:   Fri, 19 Aug 2022 13:11:43 +0200
From:   Danilo Krummrich <dakr@...hat.com>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     daniel@...ll.ch, airlied@...ux.ie, tzimmermann@...e.de,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH drm-misc-next 2/3] drm/vc4: plane: protect device
 resources after removal

Hi Maxime,

On 8/19/22 09:26, Maxime Ripard wrote:
> Hi,
> 
> On Fri, Aug 19, 2022 at 02:29:04AM +0200, Danilo Krummrich wrote:
>> (Hardware) resources which are bound to the driver and device lifecycle
>> must not be accessed after the device and driver are unbound.
>>
>> However, the DRM device isn't freed as long as the last user closed it,
>> hence userspace can still call into the driver.
>>
>> Therefore protect the critical sections which are accessing those
>> resources with drm_dev_enter() and drm_dev_exit().
> 
> Ah good catch, thanks
> 
>> Fixes: 9872c7a31921 ("drm/vc4: plane: Switch to drmm_universal_plane_alloc()")
>> Signed-off-by: Danilo Krummrich <dakr@...hat.com>
>> ---
>>   drivers/gpu/drm/vc4/vc4_drv.h   |  1 +
>>   drivers/gpu/drm/vc4/vc4_plane.c | 25 +++++++++++++++++++++++++
>>   2 files changed, 26 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/vc4/vc4_drv.h b/drivers/gpu/drm/vc4/vc4_drv.h
>> index 418a8242691f..80da9a9337cc 100644
>> --- a/drivers/gpu/drm/vc4/vc4_drv.h
>> +++ b/drivers/gpu/drm/vc4/vc4_drv.h
>> @@ -341,6 +341,7 @@ struct vc4_hvs {
>>   
>>   struct vc4_plane {
>>   	struct drm_plane base;
>> +	struct drm_device *dev;
> 
> That pointer already exists in struct drm_plane
Oops, I've sent a v2. Also addressing your comment from the other patch.

- Danilo
> 
> Looks good otherwise
> 
> Maxime