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Commit ce01b173 authored by Chris Wilson's avatar Chris Wilson
Browse files

drm/i915/execlists: Assert there are no simple cycles in the dependencies 



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: default avatarChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: default avatarMichał Winiarski <michal.winiarski@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180102151235.3949-10-chris@chris-wilson.co.uk
parent 83cc84c5

drivers/gpu/drm/i915/intel_lrc.c

+8 −3
Original line number Diff line number Diff line
@@ -1011,7 +1011,8 @@ 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) {
@@ -1031,12 +1032,15 @@ 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_priotree_signaled(p->signaler))

				continue;
@@ -1048,7 +1052,8 @@ 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.