On 06/02/2020 15:29, Chris Wilson wrote:
Quoting Chris Wilson (2020-02-06 15:23:25)
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 virtal_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.ursu...@intel.com>
Fixes: dc93c9b69315 ("drm/i915/gt: Schedule request retirement when signaler 
idles")
Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursu...@intel.com>

Alternatively we could fixup the rq->engine before
__i915_request_submit. That would stop the spread of
intel_virtual_engine_get_sibling().

This is likely to be the cleaner fix, so I think I would prefer this and
then remove the get_sibling().

Yes it makes more sense for rq->engine to be always physical at the point of __i915_request_submit.

Regards,

Tvrtko


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