[PATCH v2] drm: Do not call drm_dev_unregister twice on drm_unplug_dev

[Hans de Goede]

Hi,

On 29-05-17 21:02, Daniel Vetter wrote:
> On Sun, May 28, 2017 at 07:16:55PM +0200, Hans de Goede wrote:
>> Since commit a39be606f99d ("drm: Do a full device unregister when
>> unplugging") drm_unplug_dev has been calling drm_dev_unregister followed
>> by a drm_put_dev when open_count reaches 0. This drm_put_dev calls
>> drm_dev_unregister again. Since drm_dev_unregister is not protected
>> against being called multiple times this leads to havoc.
>>
>> This commit fixes this by calling drm_dev_unref instead of drm_put_dev.
>>
>> Fixes: a39be606f99d ("drm: Do a full device unregister when unplugging")
>> Cc: Chris Wilson <chris at chris-wilson.co.uk>
>> Cc: Marco Diego Aurélio Mesquita <marcodiegomesquita at gmail.com>
>> Reported-by: Marco Diego Aurélio Mesquita <marcodiegomesquita at gmail.com>
>> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
>> ---
>> Note I don't have any USB display devices at hand for testing atm so
>> this patch has only been compile tested.
>> ---
>> Changes in v2:
>> -Remove unnecessary mutex changes
> 
> Offending patch is in 4.8 ... do we need cc: stable?

Yes I think a Cc: stable would be good.

> Does this need a bugreport link?

There is no bug-report that I know of (Marco reported the issues
to me by email). This likely fixes some crashes when unplugging
USB display link devices.

Note I plan to actually test this patch with an USB display device
tomorrow, so you may want to hold on merging this till I've got
around to testing this.

Regards,

Hans


>> ---
>>   drivers/gpu/drm/drm_drv.c  | 6 +++---
>>   drivers/gpu/drm/drm_file.c | 2 +-
>>   2 files changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
>> index b5c6bb46a425..30b5382bf877 100644
>> --- a/drivers/gpu/drm/drm_drv.c
>> +++ b/drivers/gpu/drm/drm_drv.c
>> @@ -364,9 +364,9 @@ void drm_unplug_dev(struct drm_device *dev)
>>   
>>   	drm_device_set_unplugged(dev);
>>   
>> -	if (dev->open_count == 0) {
>> -		drm_put_dev(dev);
>> -	}
>> +	if (dev->open_count == 0)
>> +		drm_dev_unref(dev);
>> +
>>   	mutex_unlock(&drm_global_mutex);
>>   }
>>   EXPORT_SYMBOL(drm_unplug_dev);
>> diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
>> index 3783b659cd38..edba71c8ccc3 100644
>> --- a/drivers/gpu/drm/drm_file.c
>> +++ b/drivers/gpu/drm/drm_file.c
>> @@ -424,7 +424,7 @@ int drm_release(struct inode *inode, struct file *filp)
>>   	if (!--dev->open_count) {
>>   		drm_lastclose(dev);
>>   		if (drm_device_is_unplugged(dev))
>> -			drm_put_dev(dev);
>> +			drm_dev_unref(dev);
>>   	}
>>   	mutex_unlock(&drm_global_mutex);
>>   
>> -- 
>> 2.13.0
>>
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>