From 68184eb7b09640ac84aeefe31923d70d1fa07292 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Mon, 23 Sep 2019 16:28:43 +0100
Subject: drm/i915: Fixup preempt-to-busy vs reset of a virtual request
Git-commit: 68184eb7b09640ac84aeefe31923d70d1fa07292
Patch-mainline: v5.4-rc3
References: bsc#1152489

Due to the nature of preempt-to-busy the execlists active tracking and
the schedule queue may become temporarily desync'ed (between resubmission
to HW and its ack from HW). This means that we may have unwound a
request and passed it back to the virtual engine, but it is still
inflight on the HW and may even result in a GPU hang. If we detect that
GPU hang and try to reset, the hanging request->engine will no longer
match the current engine, which means that the request is not on the
execlists active list and we should not try to find an older incomplete
request. Given that we have deduced this must be a request on a virtual
engine, it is the single active request in the context and so must be
guilty (as the context is still inflight, it is prevented from being
executed on another engine as we process the reset).

Fixes: 22b7a426bbe1 ("drm/i915/execlists: Preempt-to-busy")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190923152844.8914-2-chris@chris-wilson.co.uk
(cherry picked from commit cb2377a919bbe8107af269c5a31a8d5cfb27d867)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/gpu/drm/i915/gt/intel_lrc.c   | 6 +++++-
 drivers/gpu/drm/i915/gt/intel_reset.c | 4 +---
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index b9520319684a..b09bd1729d39 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -2414,10 +2414,14 @@ static void reset_csb_pointers(struct intel_engine_cs *engine)
 
 static struct i915_request *active_request(struct i915_request *rq)
 {
-	const struct list_head * const list = &rq->timeline->requests;
 	const struct intel_context * const ce = rq->hw_context;
 	struct i915_request *active = NULL;
+	struct list_head *list;
 
+	if (!i915_request_is_active(rq)) /* unwound, but incomplete! */
+		return rq;
+
+	list = &rq->timeline->requests;
 	list_for_each_entry_from_reverse(rq, list, link) {
 		if (i915_request_completed(rq))
 			break;
diff --git a/drivers/gpu/drm/i915/gt/intel_reset.c b/drivers/gpu/drm/i915/gt/intel_reset.c
index eeb3bd0c4d69..8cea42379dd7 100644
--- a/drivers/gpu/drm/i915/gt/intel_reset.c
+++ b/drivers/gpu/drm/i915/gt/intel_reset.c
@@ -42,11 +42,10 @@ static void engine_skip_context(struct i915_request *rq)
 	struct intel_engine_cs *engine = rq->engine;
 	struct i915_gem_context *hung_ctx = rq->gem_context;
 
-	lockdep_assert_held(&engine->active.lock);
-
 	if (!i915_request_is_active(rq))
 		return;
 
+	lockdep_assert_held(&engine->active.lock);
 	list_for_each_entry_continue(rq, &engine->active.requests, sched.link)
 		if (rq->gem_context == hung_ctx)
 			i915_request_skip(rq, -EIO);
@@ -123,7 +122,6 @@ void __i915_request_reset(struct i915_request *rq, bool guilty)
 		  rq->fence.seqno,
 		  yesno(guilty));
 
-	lockdep_assert_held(&rq->engine->active.lock);
 	GEM_BUG_ON(i915_request_completed(rq));
 
 	if (guilty) {
-- 
2.28.0