The dependency chain must be an acyclic graph. This is checked by the
swfence, but for sanity, also do a simple check that we do not corrupt
our list iteration in execlists_schedule() by a shallow dependency
cycle.
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/intel_lrc.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 007aec9d95c9..8c9d6cef2482 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1006,7 +1006,8 @@ static void execlists_schedule(struct drm_i915_gem_request *request, int prio)
stack.signaler = &request->priotree;
list_add(&stack.dfs_link, &dfs);
- /* Recursively bump all dependent priorities to match the new request.
+ /*
+ * Recursively bump all dependent priorities to match the new request.
*
* A naive approach would be to use recursion:
* static void update_priorities(struct i915_priotree *pt, prio) {
@@ -1026,12 +1027,15 @@ static void execlists_schedule(struct drm_i915_gem_request *request, int prio)
list_for_each_entry_safe(dep, p, &dfs, dfs_link) {
struct i915_priotree *pt = dep->signaler;
- /* Within an engine, there can be no cycle, but we may
+ /*
+ * Within an engine, there can be no cycle, but we may
* refer to the same dependency chain multiple times
* (redundant dependencies are not eliminated) and across
* engines.
*/
list_for_each_entry(p, &pt->signalers_list, signal_link) {
+ GEM_BUG_ON(p == dep); /* no cycles! */
+
if (i915_gem_request_completed(priotree_to_request(p->signaler)))
continue;
@@ -1043,7 +1047,8 @@ static void execlists_schedule(struct drm_i915_gem_request *request, int prio)
list_safe_reset_next(dep, p, dfs_link);
}
- /* If we didn't need to bump any existing priorities, and we haven't
+ /*
+ * 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
* execlists_submit_request()), we can set our own priority and skip
* acquiring the engine locks.
--
2.15.1
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