When reprioritising a request, we build a list of its dependencies in
topological order. This should leave our origin request as the first
element in our list, if it moves we have a dependency cycle and severe
breakage. Assert that it doesn't move.
Complete, but expensive checking is done by swfence, this assert is more
about documenting the topologically ordered list.
Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: Michał Winiarski <michal.winiar...@intel.com>
---
drivers/gpu/drm/i915/intel_lrc.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 4e150b095a11..42705e3875cd 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1050,6 +1050,13 @@ static void execlists_schedule(struct
drm_i915_gem_request *request, int prio)
}
}
+ /*
+ * We should never have a dep cycle back to ourselves, leaving
+ * the original request as the origin of our topologically sorted
+ * list.
+ */
+ GEM_BUG_ON(list_first_entry(&dfs, typeof(stack), dfs_link) != &stack);
+
/*
* If we didn't need to bump any existing priorities, and we haven't
* yet submitted this request (i.e. there is no potential race with
--
2.15.1
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