On 06/02/2020 20:49, Chris Wilson wrote:
Virtual engines are fleeting. They carry a reference count and may be freed
when their last request is retired. This makes them unsuitable for the
task of housing engine->retire.work so assert that it is not used.
Tvrtko tracked down an instance where we did indeed violate this rule.
In virtual_submit_request, we flush a completed request directly with
__i915_request_submit and this causes us to queue that request on the
veng's breadcrumb list and signal it. Leading us down a path where we
should not attach the retire.
Reported-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Fixes: dc93c9b69315 ("drm/i915/gt: Schedule request retirement when signaler idles")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
drivers/gpu/drm/i915/gt/intel_breadcrumbs.c | 3 +++
drivers/gpu/drm/i915/gt/intel_gt_requests.c | 3 +++
2 files changed, 6 insertions(+)
diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
index 0ba524a414c6..cbad7fe722ce 100644
--- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
@@ -136,6 +136,9 @@ static void add_retire(struct intel_breadcrumbs *b, struct intel_timeline *tl)
struct intel_engine_cs *engine =
container_of(b, struct intel_engine_cs, breadcrumbs);
+ if (unlikely(intel_engine_is_virtual(engine)))
+ engine = intel_virtual_engine_get_sibling(engine, 0);
+
intel_engine_add_retire(engine, tl);
}
diff --git a/drivers/gpu/drm/i915/gt/intel_gt_requests.c b/drivers/gpu/drm/i915/gt/intel_gt_requests.c
index 7ef1d37970f6..8a5054f21bf8 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt_requests.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt_requests.c
@@ -99,6 +99,9 @@ static bool add_retire(struct intel_engine_cs *engine,
void intel_engine_add_retire(struct intel_engine_cs *engine,
struct intel_timeline *tl)
{
+ /* We don't deal well with the engine disappearing beneath us */
+ GEM_BUG_ON(intel_engine_is_virtual(engine));
+
if (add_retire(engine, tl))
schedule_work(&engine->retire_work);
}
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Regards,
Tvrtko
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