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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
    >
    >
    Jesse,

    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?

    Thomas




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