Re: [PATCH v3 8/9] drm/rockchip: gem: Don't alloc/free gem buf when dev_private is invalid

[jeffy <jeffy.chen@rock-chips.com>]

Hi Sean,

On 04/06/2017 12:28 AM, Sean Paul wrote:
> On Wed, Apr 05, 2017 at 04:29:26PM +0800, Jeffy Chen wrote:
>> After unbinding drm, the userspace may still has a chance to access
>> gem buf.
>>
>> Add a sanity check for a NULL dev_private to prevent that from
>> happening.
>
> I still don't understand how this is happening. You're saying that these hooks
> can be called after rockchip_drm_unbind() has finished?
>
yes, tested on chromebook rk3399 kevin with kernel 4.4, if trigger 
unbind without killing display service(ui or frecon):

[   31.276889] [<ffffffc0002089e4>] dump_backtrace+0x0/0x164
[   31.282288] [<ffffffc000208b6c>] show_stack+0x24/0x30
[   31.287338] [<ffffffc0004be028>] dump_stack+0x98/0xb8
[   31.292389] [<ffffffc0005c0b8c>] rockchip_gem_create_object+0x6c/0x2ec
[   31.298910] [<ffffffc0005c0fa0>] 
rockchip_gem_create_with_handle+0x38/0x10c
[   31.305868] [<ffffffc0005c12b8>] rockchip_gem_create_ioctl+0x38/0x50
[   31.312221] [<ffffffc000598844>] drm_ioctl+0x2bc/0x438
[   31.317359] [<ffffffc0005b5ee0>] drm_compat_ioctl+0x3c/0x70
[   31.322935] [<ffffffc0003a6960>] compat_SyS_ioctl+0x134/0x1048
[   31.328766] [<ffffffc000203e90>] __sys_trace_return+0x0/0x4

> Sean
>
>>
>> Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
>> ---
>>
>> Changes in v3:
>> Address Daniel Vetter <daniel@ffwll.ch>'s comments.
>> Update commit message.
>>
>> Changes in v2: None
>>
>>   drivers/gpu/drm/rockchip/rockchip_drm_gem.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
>> index df9e570..205a3dc 100644
>> --- a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
>> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
>> @@ -184,6 +184,9 @@ static int rockchip_gem_alloc_buf(struct rockchip_gem_object *rk_obj,
>>   	struct drm_device *drm = obj->dev;
>>   	struct rockchip_drm_private *private = drm->dev_private;
>>
>> +	if (!private)
>> +		return -ENODEV;
>> +
>>   	if (private->domain)
>>   		return rockchip_gem_alloc_iommu(rk_obj, alloc_kmap);
>>   	else
>> @@ -208,6 +211,11 @@ static void rockchip_gem_free_dma(struct rockchip_gem_object *rk_obj)
>>
>>   static void rockchip_gem_free_buf(struct rockchip_gem_object *rk_obj)
>>   {
>> +	struct drm_device *drm = rk_obj->base.dev;
>> +
>> +	if (!drm->dev_private)
>> +		return;
>> +
>>   	if (rk_obj->pages)
>>   		rockchip_gem_free_iommu(rk_obj);
>>   	else
>> --
>> 2.1.4
>>
>