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You quoted the wrong code, this is what really matters: drm_sched_wqueue_stop(sched); for (i = DRM_SCHED_PRIORITY_KERNEL; i < sched->num_rqs; i++) kfree(sched->sched_rq[i]); >> >> for (i = DRM_SCHED_PRIORITY_KERNEL; i < sched->num_rqs; i++) >> kfree(sched->sched_rq[i]); >> >> /* Wakeup everyone stuck in drm_sched_entity_flush for this scheduler */ >> wake_up_all(&sched->job_scheduled); That was an extremely ugly hack applied long long time ago because amdgpu was broken at that time and didn't waited for drm_sched_entity_flush()/drm_sched_entity_fini() before calling drm_sched_fini(). >> >> A KUnit case that keeps the TDR inside timedout_job() while drm_sched_fini() >> runs, with the callback calling drm_sched_increase_karma() as amdgpu does: Amdgpu shouldn't do that any more. It is perfectly possible that we still have a bug in the driver teardown during hot remove, but we certainly shouldn't work around that by adding such hacks to the scheduler. > > How precisely are you reproducing the problem? I'm wondering why it > wasn't observed sooner. > > Since you mention amdgpu, many of the twirks in the drm_sched code base > were added to work around ordering problems in that driver. > > The drm_sched life time rules are: > > 1. All fences returned through ops->run_job() must be signaled by > the driver before calling drm_sched_fini(). > 2. Entities must be torn down before the scheduler. > > IOW, I would dare to say that the wake_up_all() maybe shouldn't even > exist in an ideal world, because the driver would never call > drm_sched_fini() while it's still blocking in drm_sched_entity_flush(). > Maybe Christian has some wisdom on the background. Yes, exactly that. This line should potentially just be removed. Regards, Christian. > >> >>   BUG: KASAN: slab-use-after-free in _raw_spin_lock+0x2b/0x40 >>   Workqueue: events drm_sched_job_timedout >>    drm_sched_increase_karma+0x138/0x3e0 >>    fini_uaf_timedout_job+0x4c/0x140 >>    drm_sched_job_timedout+0x1b4/0x620 >>   allocated by drm_sched_init+0x49c, freed by drm_sched_fini+0xec >> >> Moving the loop down beside kfree(sched->sched_rq) silences it, and nothing >> between the two positions reads the run queues. Is that the right fix, or is >> the intended rule that the TDR can never still be running at that point? > > Can you post a patch or RFC patch for fixing it? It's easier to discuss > then. I think I get what you mean, and it's probably the best cost- > benefit-ratio fix. I'd then just put some brain power into > understanding the ordering between threads though > > > > Regards > P.