When importing a BO, if it is already imported, then the handle will
alias an existing BO instance. It is possible for the existing owner to
free the BO after the import and leave a dangling handle before we get a
chance to increase the refcount, so we need to lock the BO table mutex
before importing, to make sure nobody else goes through the free path
during that window.
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Signed-off-by: Asahi Lina <lina@asahilina.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20403>
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