On 13/07/2020 15:16, Chris Wilson wrote:
Preempt-to-busy introduces various fascinating complications in that the requests may complete as we are unsubmitting them from HW. As they may then signal after unsubmission, we may find ourselves having to cleanup the signaling request from within the signaling callback. This causes us to recurse onto the same i915_request.lock.
However, if the request is already signaled (as it will be before we enter the signal callbacks), we know we can skip the signaling of that request during submission, neatly evading the spinlock recursion.
unsubmit(ve.rq0) # timeslice expiration or other preemption -> virtual_submit_request(ve.rq0) dma_fence_signal(ve.rq0) # request completed before preemption ack -> submit_notify(ve.rq1) -> virtual_submit_request(ve.rq1) # sees that we have completed ve.rq0 -> __i915_request_submit(ve.rq0)
[ 264.210142] BUG: spinlock recursion on CPU#2, sample_multi_tr/2093 [ 264.210150] lock: 0xffff9efd6ac55080, .magic: dead4ead, .owner: sample_multi_tr/2093, .owner_cpu: 2 [ 264.210155] CPU: 2 PID: 2093 Comm: sample_multi_tr Tainted: G U [ 264.210158] Hardware name: Intel Corporation CoffeeLake Client Platform/CoffeeLake S UDIMM RVP, BIOS CNLSFWR1.R00.X212.B01.1909060036 09/06/2019 [ 264.210160] Call Trace: [ 264.210167] dump_stack+0x98/0xda [ 264.210174] spin_dump.cold+0x24/0x3c [ 264.210178] do_raw_spin_lock+0x9a/0xd0 [ 264.210184] _raw_spin_lock_nested+0x6a/0x70 [ 264.210314] __i915_request_submit+0x10a/0x3c0 [i915] [ 264.210415] virtual_submit_request+0x9b/0x380 [i915] [ 264.210516] submit_notify+0xaf/0x14c [i915] [ 264.210602] __i915_sw_fence_complete+0x8a/0x230 [i915] [ 264.210692] i915_sw_fence_complete+0x2d/0x40 [i915] [ 264.210762] __dma_i915_sw_fence_wake+0x19/0x30 [i915] [ 264.210767] dma_fence_signal_locked+0xb1/0x1c0 [ 264.210772] dma_fence_signal+0x29/0x50 [ 264.210871] i915_request_wait+0x5cb/0x830 [i915] [ 264.210876] ? dma_resv_get_fences_rcu+0x294/0x5d0 [ 264.210974] i915_gem_object_wait_fence+0x2f/0x40 [i915] [ 264.211084] i915_gem_object_wait+0xce/0x400 [i915] [ 264.211178] i915_gem_wait_ioctl+0xff/0x290 [i915]
Signed-off-by: Chris Wilson chris@chris-wilson.co.uk Fixes: 22b7a426bbe1 ("drm/i915/execlists: Preempt-to-busy") References: 6d06779e8672 ("drm/i915: Load balancing across a virtual engine") Signed-off-by: Chris Wilson chris@chris-wilson.co.uk Cc: Tvrtko Ursulin tvrtko.ursulin@intel.com Cc: "Nayana, Venkata Ramana" venkata.ramana.nayana@intel.com Cc: stable@vger.kernel.org # v5.4+
drivers/gpu/drm/i915/gt/intel_breadcrumbs.c | 7 ++++++- drivers/gpu/drm/i915/i915_request.c | 23 ++++++++++++--------- 2 files changed, 19 insertions(+), 11 deletions(-)
diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c index d907d538176e..91786310c114 100644 --- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c +++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c @@ -314,13 +314,18 @@ bool i915_request_enable_breadcrumb(struct i915_request *rq) { lockdep_assert_held(&rq->lock);
- if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &rq->fence.flags))
return true;- if (test_bit(I915_FENCE_FLAG_ACTIVE, &rq->fence.flags)) { struct intel_breadcrumbs *b = &rq->engine->breadcrumbs; struct intel_context *ce = rq->context; struct list_head *pos;
spin_lock(&b->irq_lock);
GEM_BUG_ON(test_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags));
if (test_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags))goto unlock;if (!__intel_breadcrumbs_arm_irq(b)) goto unlock; diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c index 3bb7320249ae..0b2fe55e6194 100644 --- a/drivers/gpu/drm/i915/i915_request.c +++ b/drivers/gpu/drm/i915/i915_request.c @@ -560,22 +560,25 @@ bool __i915_request_submit(struct i915_request *request) engine->serial++; result = true; -xfer: /* We may be recursing from the signal callback of another i915 fence */
- spin_lock_nested(&request->lock, SINGLE_DEPTH_NESTING);
+xfer: if (!test_and_set_bit(I915_FENCE_FLAG_ACTIVE, &request->fence.flags)) { list_move_tail(&request->sched.link, &engine->active.requests); clear_bit(I915_FENCE_FLAG_PQUEUE, &request->fence.flags);
__notify_execute_cb(request);- GEM_BUG_ON(!llist_empty(&request->execute_cb));
- if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &request->fence.flags) &&
!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &request->fence.flags) &&!i915_request_enable_breadcrumb(request))intel_engine_signal_breadcrumbs(engine);
- /* We may be recursing from the signal callback of another i915 fence */
- if (!i915_request_signaled(request)) {
spin_lock_nested(&request->lock, SINGLE_DEPTH_NESTING);__notify_execute_cb(request);if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,&request->fence.flags) &&!i915_request_enable_breadcrumb(request))intel_engine_signal_breadcrumbs(engine);
- spin_unlock(&request->lock);
spin_unlock(&request->lock);GEM_BUG_ON(!llist_empty(&request->execute_cb));- }
return result; }
Reviewed-by: Tvrtko Ursulin tvrtko.ursulin@intel.com
Regards,
Tvrtko