On 21/09/2019 10:55, Chris Wilson wrote:
As preempt-to-busy leaves the request on the HW as the resubmission is
processed, that request may complete in the background and even cause a
second virtual request to enter queue. This second virtual request
breaks our "single request in the virtual pipeline" assumptions.
Furthermore, as the virtual request may be completed and retired, we
lose the reference the virtual engine assumes is held. Normally, just
removing the request from the scheduler queue removes it from the
engine, but the virtual engine keeps track of its singleton request via
its ve->request. This pointer needs protecting with a reference.
Fixes: 22b7a426bbe1 ("drm/i915/execlists: Preempt-to-busy")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
drivers/gpu/drm/i915/gt/intel_lrc.c | 34 ++++++++++++++++++++++-------
1 file changed, 26 insertions(+), 8 deletions(-)
diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 53bc4308793c..1b2bacc60300 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -529,7 +529,6 @@ __unwind_incomplete_requests(struct intel_engine_cs *engine)
i915_request_cancel_breadcrumb(rq);
spin_unlock(&rq->lock);
}
- rq->engine = owner;
owner->submit_request(rq);
active = NULL;
}
@@ -1248,6 +1247,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
submit = true;
last = rq;
}
+ i915_request_put(rq);
if (!submit) {
spin_unlock(&ve->base.active.lock);
@@ -2535,6 +2535,7 @@ static void execlists_cancel_requests(struct intel_engine_cs *engine)
rq->engine = engine;
__i915_request_submit(rq);
+ i915_request_put(rq);
ve->base.execlists.queue_priority_hint = INT_MIN;
}
@@ -3787,7 +3788,9 @@ static void virtual_submission_tasklet(unsigned long data)
static void virtual_submit_request(struct i915_request *rq)
{
- struct virtual_engine *ve = to_virtual_engine(rq->engine);
+ struct virtual_engine *ve = to_virtual_engine(rq->hw_context->engine);
+ struct i915_request *stale;
+ unsigned long flags;
GEM_TRACE("%s: rq=%llx:%lld\n",
ve->base.name,
@@ -3796,15 +3799,30 @@ static void virtual_submit_request(struct i915_request *rq)
GEM_BUG_ON(ve->base.submit_request != virtual_submit_request);
- GEM_BUG_ON(ve->request);
- GEM_BUG_ON(!list_empty(virtual_queue(ve)));
+ spin_lock_irqsave(&ve->base.active.lock, flags);
+
+ stale = ve->request;
fetch_and_zero so you don't have to set it to NULL a bit lower?
s/stale/completed/, plus a comment describing preempt-to-busy is to blame?
+ if (stale) {
+ GEM_BUG_ON(!i915_request_completed(stale));
+ __i915_request_submit(stale);
+ i915_request_put(stale);
+ }
+
+ if (i915_request_completed(rq)) {
+ __i915_request_submit(rq);
+ ve->request = NULL;
+ } else {
+ ve->base.execlists.queue_priority_hint = rq_prio(rq);
+ ve->request = i915_request_get(rq);
+ rq->engine = &ve->base; /* fixup from unwind */
The last line has me confused. Isn't this the normal veng rq submission
path? In which case eq->engine will already be set to veng. But on the
unwind path you have removed reset-back of rq->engine to owner. Ah.. the
unwind calls veng->submit_request on it, and then we end up in here..
Okay, this is outside the normal path, I mean the else block has two
functions/paths, and this should be explained in a comment.
- ve->base.execlists.queue_priority_hint = rq_prio(rq);
- WRITE_ONCE(ve->request, rq);
+ GEM_BUG_ON(!list_empty(virtual_queue(ve)));
+ list_move_tail(&rq->sched.link, virtual_queue(ve));
- list_move_tail(&rq->sched.link, virtual_queue(ve));
+ tasklet_schedule(&ve->base.execlists.tasklet);
+ }
- tasklet_schedule(&ve->base.execlists.tasklet);
+ spin_unlock_irqrestore(&ve->base.active.lock, flags);
}
static struct ve_bond *
Otherwise I *think* it's okay.
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Regards,
Tvrtko
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