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SubjectRe: Gem GTT mmaps..
Jesse Barnes wrote:
> On Friday, February 6, 2009 1:35 pm Thomas Hellström wrote:
>> Jesse Barnes wrote:
>>> On Thursday, February 5, 2009 10:37 am Jesse Barnes wrote:
>>>> So if we leave the lookup reference around from the GTT mapping ioctl,
>>>> that would take care of new mappings. And if we added/removed
>>>> references at VM open/close time, we should be covered for fork. But is
>>>> it ok to add a new unref in the finish ioctl for GTT mapped objects? I
>>>> don't think so, because we don't know for sure if the caller was the one
>>>> that created the new fake offset (which would be one way of detecting
>>>> whether it was GTT mapped). Seems like we need a new unmap ioctl? Or we
>>>> could put the mapping ref/unref in libdrm, where it would be tracked on
>>>> a per-process basis...
>>> Ah but maybe we should just tear down the fake offset at unmap time; then
>>> we'd be able to use it as an existence test for the mapping and get the
>>> refcounting right. The last thing I thought of was whether we'd be ok in
>>> a map_gtt -> crash case. I *think* the vm_close code will deal with
>>> that, if we do a deref there?
>> Yes, an mmap() is always paired with a vm_close(), and the vm_close()
>> also happens in a crash situation.
> This one should cover the cases you found.
> - ref at map time will keep the object around so fault shouldn't fail
> - additional threads will take their refs in vm_open/close
> - unmap will unref and remove mmap_offset allowing object to be freed

Yes, it looks OK to me.
A short question, though, when is i915_gem_sw_finish_ioctl called? Is it
possible that the client may still think its mmap offset is valid?


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