From ff08ff01993c9c0fb5d792bfb87e4074f764324f Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Thu, 20 Feb 2020 07:50:20 +0000
Subject: drm/i915/gt: Protect signaler walk with RCU
Git-commit: 66940061a52fba730fdb49e133502e19be684202
Patch-mainline: v5.7-rc1
References: jsc#SLE-12680, jsc#SLE-12880, jsc#SLE-12882, jsc#SLE-12883, jsc#SLE-13496, jsc#SLE-15322

While we know that the waiters cannot disappear as we walk our list
(only that they might be added), the same cannot be said for our
signalers as they may be completed by the HW and retired as we process
this request. Ergo we need to use rcu to protect the list iteration and
remember to mark up the list_del_rcu.

v2: Mark the deps as safe-for-rcu

Fixes: 793c22617367 ("drm/i915/gt: Protect execlists_hold/unhold from new waiters")
Fixes: 32ff621fd744 ("drm/i915/gt: Allow temporary suspension of inflight requests")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200220075025.1539375-1-chris@chris-wilson.co.uk
Signed-off-by: Patrik Jakobsson <pjakobsson@suse.de>
---
 drivers/gpu/drm/i915/gt/intel_lrc.c   | 16 ++++++++++------
 drivers/gpu/drm/i915/i915_scheduler.c |  7 ++++---
 2 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 3d5293a32ee0..bb240f5a9885 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -1657,9 +1657,9 @@ static void virtual_xfer_breadcrumbs(struct virtual_engine *ve,
 				     wait_link)
 
 #define for_each_signaler(p__, rq__) \
-	list_for_each_entry_lockless(p__, \
-				     &(rq__)->sched.signalers_list, \
-				     signal_link)
+	list_for_each_entry_rcu(p__, \
+				&(rq__)->sched.signalers_list, \
+				signal_link)
 
 static void defer_request(struct i915_request *rq, struct list_head * const pl)
 {
@@ -2532,11 +2532,13 @@ static bool execlists_hold(struct intel_engine_cs *engine,
 static bool hold_request(const struct i915_request *rq)
 {
 	struct i915_dependency *p;
+	bool result = false;
 
 	/*
 	 * If one of our ancestors is on hold, we must also be on hold,
 	 * otherwise we will bypass it and execute before it.
 	 */
+	rcu_read_lock();
 	for_each_signaler(p, rq) {
 		const struct i915_request *s =
 			container_of(p->signaler, typeof(*s), sched);
@@ -2544,11 +2546,13 @@ static bool hold_request(const struct i915_request *rq)
 		if (s->engine != rq->engine)
 			continue;
 
-		if (i915_request_on_hold(s))
-			return true;
+		result = i915_request_on_hold(s);
+		if (result)
+			break;
 	}
+	rcu_read_unlock();
 
-	return false;
+	return result;
 }
 
 static void __execlists_unhold(struct i915_request *rq)
diff --git a/drivers/gpu/drm/i915/i915_scheduler.c b/drivers/gpu/drm/i915/i915_scheduler.c
index e19a37a83397..59f70b674665 100644
--- a/drivers/gpu/drm/i915/i915_scheduler.c
+++ b/drivers/gpu/drm/i915/i915_scheduler.c
@@ -486,7 +486,7 @@ void i915_sched_node_fini(struct i915_sched_node *node)
 	list_for_each_entry_safe(dep, tmp, &node->signalers_list, signal_link) {
 		GEM_BUG_ON(!list_empty(&dep->dfs_link));
 
-		list_del(&dep->wait_link);
+		list_del_rcu(&dep->wait_link);
 		if (dep->flags & I915_DEPENDENCY_ALLOC)
 			i915_dependency_free(dep);
 	}
@@ -497,7 +497,7 @@ void i915_sched_node_fini(struct i915_sched_node *node)
 		GEM_BUG_ON(dep->signaler != node);
 		GEM_BUG_ON(!list_empty(&dep->dfs_link));
 
-		list_del(&dep->signal_link);
+		list_del_rcu(&dep->signal_link);
 		if (dep->flags & I915_DEPENDENCY_ALLOC)
 			i915_dependency_free(dep);
 	}
@@ -526,7 +526,8 @@ static struct i915_global_scheduler global = { {
 int __init i915_global_scheduler_init(void)
 {
 	global.slab_dependencies = KMEM_CACHE(i915_dependency,
-					      SLAB_HWCACHE_ALIGN);
+					      SLAB_HWCACHE_ALIGN |
+					      SLAB_TYPESAFE_BY_RCU);
 	if (!global.slab_dependencies)
 		return -ENOMEM;
 
-- 
2.28.0