[Intel-gfx] [PATCH] drm/i915: Defer semaphore priority bumping to a workqueue

[Chris Wilson]

Quoting Chris Wilson (2020-03-10 10:17:20)
> Since the semaphore fence may be signaled from inside an interrupt
> handler from inside a request holding its request->lock, we cannot then
> enter into the engine->active.lock for processing the semaphore priority
> bump as we may traverse our call tree and end up on another held
> request.
> 
> CPU 0:
> [ 2243.218864]  _raw_spin_lock_irqsave+0x9a/0xb0
> [ 2243.218867]  i915_schedule_bump_priority+0x49/0x80 [i915]
> [ 2243.218869]  semaphore_notify+0x6d/0x98 [i915]
> [ 2243.218871]  __i915_sw_fence_complete+0x61/0x420 [i915]
> [ 2243.218874]  ? kmem_cache_free+0x211/0x290
> [ 2243.218876]  i915_sw_fence_complete+0x58/0x80 [i915]
> [ 2243.218879]  dma_i915_sw_fence_wake+0x3e/0x80 [i915]
> [ 2243.218881]  signal_irq_work+0x571/0x690 [i915]
> [ 2243.218883]  irq_work_run_list+0xd7/0x120
> [ 2243.218885]  irq_work_run+0x1d/0x50
> [ 2243.218887]  smp_irq_work_interrupt+0x21/0x30
> [ 2243.218889]  irq_work_interrupt+0xf/0x20
> 
> CPU 1:
> [ 2242.173107]  _raw_spin_lock+0x8f/0xa0
> [ 2242.173110]  __i915_request_submit+0x64/0x4a0 [i915]
> [ 2242.173112]  __execlists_submission_tasklet+0x8ee/0x2120 [i915]
> [ 2242.173114]  ? i915_sched_lookup_priolist+0x1e3/0x2b0 [i915]
> [ 2242.173117]  execlists_submit_request+0x2e8/0x2f0 [i915]
> [ 2242.173119]  submit_notify+0x8f/0xc0 [i915]
> [ 2242.173121]  __i915_sw_fence_complete+0x61/0x420 [i915]
> [ 2242.173124]  ? _raw_spin_unlock_irqrestore+0x39/0x40
> [ 2242.173137]  i915_sw_fence_complete+0x58/0x80 [i915]
> [ 2242.173140]  i915_sw_fence_commit+0x16/0x20 [i915]
> 
> CPU 2:
> [ 2242.173107]  _raw_spin_lock+0x8f/0xa0
> [ 2242.173110]  __i915_request_submit+0x64/0x4a0 [i915]
> [ 2242.173112]  __execlists_submission_tasklet+0x8ee/0x2120 [i915]
> [ 2242.173114]  ? i915_sched_lookup_priolist+0x1e3/0x2b0 [i915]
> [ 2242.173117]  execlists_submit_request+0x2e8/0x2f0 [i915]
> [ 2242.173119]  submit_notify+0x8f/0xc0 [i915]

Ignore this, I thought this was a third interesting chunk, but I copied
the same one twice.
-Chris