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 03:07 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.

> userptr->pages. In this instance userptr->pages doesn't get populated
> before the MAP_FIXED anyway.

Hmmm... did not even think about that. Why does MAP_FIXED trigger get_pages?

Tvrtko
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