[amdgpu] quitting a compositor often locks the driver up

[Val Packett]

Lockups on quitting the window server (making the window server completely unkillable) on amdgpu have been an issue since forever and it's still an issue on 5.2.

Currently the hanging stack trace when quitting wayfire looks like:

exit1 → fdescfree → … → linux_file_close → drm_release → drm_file_free → amdgpu_driver_postclose_kms → amdgpu_vm_fini → drm_sched_entity_destroy → drm_sched_entity_flush → linux_wait_event_common → linux_add_to_sleepqueue → sleepq_wait_sig → sleepq_catch_signals → mi_switch

upd: huh, drm_sched_entity_flush is the source of the infamous ==========> BUG: entity->rq->sched is NULL print

upd: so this is supposed to time out in 1000ms but doesn't

[Val Packett]

oh, that was easy: https://reviews.freebsd.org/D25509

[Val Packett]

Landed as rS362829