[Intel-gfx] [PATCH] drm/i915: Neuter virtual rq->engine on retire
chris at chris-wilson.co.uk
Tue May 19 14:51:31 UTC 2020
We do not hold a reference to rq->engine, and so if it is a virtual
engine it may have already been freed by the time we free the request.
The last reference we hold on the virtual engine is via rq->context,
and that is released on request retirement. So if we find ourselves
retiring a virtual request, redirect it to a real sibling.
Fixes: 43acd6516ca9 ("drm/i915: Keep a per-engine request pool")
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
drivers/gpu/drm/i915/i915_request.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
index 31ef683d27b4..a816218cc693 100644
@@ -242,9 +242,26 @@ static void remove_from_engine(struct i915_request *rq)
locked = engine;
+ * During i915_fence_release we stash one request on the
+ * rq->engine for use as an emergency reserve. However, we
+ * neither want to keep a request on a virtual engine, nor do
+ * we hold a reference to a virtual engine at that point. So
+ * if rq->engine is virtual, replace it with a real one. Which
+ * one is immaterial at this point as the request has been
+ * retired, and if it was a virtual engine will not have any
+ * signaling or other related paraphernalia.
+ * However, it would be nice if we didn't have to...
+ if (intel_engine_is_virtual(rq->engine))
+ rq->engine = intel_virtual_engine_get_sibling(rq->engine, 0);
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