From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Tue, 2 Jan 2018 15:12:26 +0000
Subject: drm/i915/execlists: Assert there are no simple cycles in the
dependencies
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Git-commit: ce01b173773a09e2b5d3007c26d11cbd7737c3fe
Patch-mainline: v4.17-rc1
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166
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@chris-wilson.co.uk>
Reviewed-by: Michał Winiarski <michal.winiarski@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180102151235.3949-10-chris@chris-wilson.co.uk
Acked-by: Petr Tesarik <ptesarik@suse.com>
---
drivers/gpu/drm/i915/intel_lrc.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1019,7 +1019,8 @@ static void execlists_schedule(struct dr
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) {
@@ -1039,12 +1040,15 @@ static void execlists_schedule(struct dr
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;
@@ -1056,7 +1060,8 @@ static void execlists_schedule(struct dr
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.