Re: [PATCH] tests/gem_userptr_blits: subtests for MAP_FIXED mappings of regular bo

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 06/29/2015 03:25 PM, Chris Wilson wrote:
> On Mon, Jun 29, 2015 at 03:15:12PM +0100, Tvrtko Ursulin wrote:
>>
>> On 06/29/2015 03:07 PM, Chris Wilson wrote:
>>> On Mon, Jun 29, 2015 at 03:01:12PM +0100, Tvrtko Ursulin wrote:
>>>>
>>>> On 06/29/2015 11:59 AM, Michał Winiarski wrote:
>>>>> When the the memory backing the userptr object is freed by the user, it's
>>>>> possible to trigger recursive deadlock caused by operations done on
>>>>> different BO mapped in that region, triggering invalidate.
>>>>>
>>>>> Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
>>>>> ---
>>>>>   tests/gem_userptr_blits.c | 83 +++++++++++++++++++++++++++++++++++++++++++++++
>>>>>   1 file changed, 83 insertions(+)
>>>>>
>>>>> diff --git a/tests/gem_userptr_blits.c b/tests/gem_userptr_blits.c
>>>>> index 1f2cc96..3fe8f90 100644
>>>>> --- a/tests/gem_userptr_blits.c
>>>>> +++ b/tests/gem_userptr_blits.c
>>>>> @@ -640,6 +640,80 @@ static void test_forked_access(int fd)
>>>>>   	free(ptr2);
>>>>>   }
>>>>>
>>>>> +static int test_map_fixed_invalidate(int fd, bool overlap)
>>>>> +{
>>>>> +	void *ptr;
>>>>> +	void *map;
>>>>> +	int i;
>>>>> +	int num_handles = overlap ? 2 : 1;
>>>>> +	uint32_t handle[num_handles];
>>>>> +	uint32_t mmap_handle;
>>>>> +	struct drm_i915_gem_mmap_gtt mmap_arg;
>>>>> +
>>>>> +	igt_assert(posix_memalign(&ptr, PAGE_SIZE, PAGE_SIZE) == 0);
>>>>> +	for (i=0; i<num_handles; i++)
>>>>> +		igt_assert(gem_userptr(fd, ptr, PAGE_SIZE, 0, &handle[i]) == 0);
>>>>> +	free(ptr);
>>>>
>>>> I am not sure we can rely on free triggering munmap(2) here, I think
>>>> this is just glibc implementation detail. So I would suggest
>>>> allocating with mmap and freeing with munmap.
>>>
>>> The MAP_FIXED itself should be sufficient to invalidate any prior vma at
>>> that address, so we don't depend upon the free() here to zap
>>
>> Yeah, but does the free trigger an invalidate, or does it not? Or in
>> other words, is the one from MAP_FIXED the first one, or not? Better
>> to be explicit than undefined in the test case, that was my point.
>
> Yes. But I would prefer MAP_FIXED to be the first invalidate, but that
> looks like we then need to leak the ptr.

If it used mmap instead of posix_memalign and no free then what would it 
leak? MAP_FIXED would be guaranteed first invalidate and it would 
discard the mapping.

Tvrtko



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