Re: [PATCH 1/2] drm/ttm: set ttm_buffer_object pointer as null after it's freed

["Christian König" <christian.koenig-5C7GfCeVMHo@public.gmane.org>]

Am 10.09.2018 um 11:23 schrieb Huang Rui:
> On Mon, Sep 10, 2018 at 11:00:04AM +0200, Christian König wrote:
>> Hi Ray,
>>
>> well those patches doesn't make sense, the pointer is only local to
>> the function.
> You're right.
> I narrowed it with gdb dump from ttm_bo_bulk_move_lru_tail+0x2b, the
> use-after-free should be in below codes:
>
> man = &bulk->tt[i].first->bdev->man[TTM_PL_TT];
> ttm_bo_bulk_move_helper(&bulk->tt[i], &man->lru[i], false);
>
> Is there a case, when orignal bo is destroyed in the bulk pos, but it
> doesn't update pos->first pointer, then we still use it during the bulk
> moving?

Only when a per VM BO is freed or the VM destroyed.

The first case should now be handled by "drm/amdgpu: set bulk_moveable 
to false when a per VM is released" and when we use a destroyed VM we 
would see other problems as well.

BTW: Just pushed this commit to the repository, should show up any second.

Christian.

>
> Thanks,
> Ray
>
>> Regards,
>> Christian.
>>
>> Am 10.09.2018 um 10:57 schrieb Huang Rui:
>>> It avoids to be refered again after freed.
>>>
>>> Signed-off-by: Huang Rui <ray.huang@amd.com>
>>> Cc: Christian König <christian.koenig@amd.com>
>>> Cc: Tom StDenis <Tom.StDenis@amd.com>
>>> ---
>>>   drivers/gpu/drm/ttm/ttm_bo.c | 1 +
>>>   1 file changed, 1 insertion(+)
>>>
>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
>>> index 138c989..d3ef5f8 100644
>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c
>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
>>> @@ -54,6 +54,7 @@ static struct attribute ttm_bo_count = {
>>>   static void ttm_bo_default_destroy(struct ttm_buffer_object *bo)
>>>   {
>>>   	kfree(bo);
>>> +	bo = NULL;
>>>   }
>>>   static inline int ttm_mem_type_from_place(const struct ttm_place *place,
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