@@ -560,9 +560,7 @@ 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);
@@ -570,12 +568,19 @@ bool __i915_request_submit(struct i915_request *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);
+
+ 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);
- spin_unlock(&request->lock);
+ spin_unlock(&request->lock);
+ }
return result;
}
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 5.4.48-prod-dg1-vn-2660+ #3 [ 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/i915_request.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-)