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drm/i915/gt: Remove virtual breadcrumb before transfer 

The issue with stale virtual breadcrumbs remain. Now we have the problem
that if the irq-signaler is still referencing the stale breadcrumb as we
transfer it to a new sibling, the list becomes spaghetti. This is a very
small window, but that doesn't stop it being hit infrequently. To
prevent the lists being tangled (the iterator starting on one engine's
b->signalers but walking onto another list), always decouple the virtual
breadcrumb on schedule-out and make sure that the walker has stepped out
of the lists.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201224135544.1713-5-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson 2020-12-24 13:55:40 +00:00
parent 6f0726b480
commit bab0557c8d
2 changed files with 18 additions and 2 deletions
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5
drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
View File

@ -451,15 +451,16 @@ void i915_request_cancel_breadcrumb(struct i915_request *rq)
{
struct intel_breadcrumbs *b = READ_ONCE(rq->engine)->breadcrumbs;
struct intel_context *ce = rq->context;
unsigned long flags;
bool release;
if (!test_and_clear_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags))
return;
spin_lock(&ce->signal_lock);
spin_lock_irqsave(&ce->signal_lock, flags);
list_del_rcu(&rq->signal_link);
release = remove_signaling_context(b, ce);
spin_unlock(&ce->signal_lock);
spin_unlock_irqrestore(&ce->signal_lock, flags);
if (release)
intel_context_put(ce);

15
drivers/gpu/drm/i915/gt/intel_execlists_submission.c
View File

@ -581,6 +581,21 @@ static inline void execlists_schedule_in(struct i915_request *rq, int idx)
static void kick_siblings(struct i915_request *rq, struct intel_context *ce)
{
struct virtual_engine *ve = container_of(ce, typeof(*ve), context);
struct intel_engine_cs *engine = rq->engine;
/* Flush concurrent rcu iterators in signal_irq_work */
if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &rq->fence.flags)) {
/*
* After this point, the rq may be transferred to a new
* sibling, so before we clear ce->inflight make sure that
* the context has been removed from the b->signalers and
* furthermore we need to make sure that the concurrent
* iterator in signal_irq_work is no longer following
* ce->signal_link.
*/
i915_request_cancel_breadcrumb(rq);
irq_work_sync(&engine->breadcrumbs->irq_work);
}
if (READ_ONCE(ve->request))
tasklet_hi_schedule(&ve->base.execlists.tasklet);