linux-kernel - Re: [PATCH v3 8/9] drm/rockchip: gem: Don't alloc/free gem buf when dev

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Message-ID: <58E63A88.4090108@rock-chips.com>
Date:   Thu, 06 Apr 2017 20:54:32 +0800
From:   jeffy <jeffy.chen@...k-chips.com>
To:     Sean Paul <seanpaul@...omium.org>
CC:     linux-kernel@...r.kernel.org, briannorris@...omium.org,
        dianders@...omium.org, tfiga@...omium.org, zyw@...k-chips.com,
        mark.yao@...k-chips.com, Heiko Stuebner <heiko@...ech.de>,
        dri-devel@...ts.freedesktop.org,
        linux-rockchip@...ts.infradead.org,
        David Airlie <airlied@...ux.ie>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 8/9] drm/rockchip: gem: Don't alloc/free gem buf when
 dev_private is invalid

Hi Sean,

On 04/06/2017 08:26 PM, Sean Paul wrote:
> On Thu, Apr 06, 2017 at 10:47:59AM +0800, jeffy wrote:
>> 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
>
> Hi Jeffy,
> I'm not suggesting this doesn't happen, I believe you :-). I'd really like to
> know *why* it happens.
>
> Are you sure that unbind has completely finished before this trace occurs?
> Perhaps this is results from a race between unbind and gem allocate?
yes, that unbind is finished. and it looks like the display server still 
holds drm dev fd(even it been deleted after unbind).

sometimes i can see it trigger ioctl even seconds later.

i'll send a patch to break drm_ioctl after unbind.
>
> Sean
>
>>
>>> Sean
>>>
>>>>
>>>> Signed-off-by: Jeffy Chen <jeffy.chen@...k-chips.com>
>>>> ---
>>>>
>>>> Changes in v3:
>>>> Address Daniel Vetter <daniel@...ll.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
>>>>
>>>
>>
>