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    SubjectRe: Gem GTT mmaps..
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    On Fri, 2009-02-06 at 14:24 -0800, 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

    sw_finish doesn't mean unmap (note that it doesn't actually unmap).

    If you want to actually unmap, that should be done with munmap.

    --
    Eric Anholt
    eric@anholt.net eric.anholt@intel.com


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