drm/i915/selftests: Use clear_and_wake_up_bit() for the per-engine reset bitlocks

Some selftests assume that nothing will attempt to grab these bitlocks
while they are held by the selftests. With GuC, for example, that is
not true because the hanging workloads may cause the GuC code to attempt
to grab them for a global reset, and that may cause it to end up
sleeping on the bit never waking up. Regardless whether that will be
the final solution for GuC, use clear_and_wake_up_bit() pending a more
thorough investigation on how this should be handled moving forward.

To be clear this needs to be a temporary solution. If we can't find
an in-kernel locking primitive to use here, we should at the very least
add lockdep annotation to these bitlocks with a thorough explanation
as to why we need to use bits.

v3:
- Use GEM_BUG_ON(test_and_set_bit()) rather than set_bit() to verify
  the assumption that nothing is holding the reset locks when we
  attempt to grab them. (Chris Wilson)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211105150146.834052-1-thomas.hellstrom@linux.intel.com

drivers/gpu/drm/i915/gt/selftest_hangcheck.c

@@ -471,7 +471,8 @@ static int igt_reset_nop_engine(void *arg)
 		count = 0;
 
 		st_engine_heartbeat_disable(engine);
-		set_bit(I915_RESET_ENGINE + id, &gt->reset.flags);
+		GEM_BUG_ON(test_and_set_bit(I915_RESET_ENGINE + id,
+					    &gt->reset.flags));
 		do {
 			int i;
 
@@ -528,7 +529,7 @@ static int igt_reset_nop_engine(void *arg)
 				break;
 			}
 		} while (time_before(jiffies, end_time));
-		clear_bit(I915_RESET_ENGINE + id, &gt->reset.flags);
+		clear_and_wake_up_bit(I915_RESET_ENGINE + id, &gt->reset.flags);
 		st_engine_heartbeat_enable(engine);
 
 		pr_info("%s(%s): %d resets\n", __func__, engine->name, count);
@@ -582,7 +583,8 @@ static int igt_reset_fail_engine(void *arg)
 		}
 
 		st_engine_heartbeat_disable(engine);
-		set_bit(I915_RESET_ENGINE + id, &gt->reset.flags);
+		GEM_BUG_ON(test_and_set_bit(I915_RESET_ENGINE + id,
+					    &gt->reset.flags));
 
 		force_reset_timeout(engine);
 		err = intel_engine_reset(engine, NULL);
@@ -679,7 +681,7 @@ static int igt_reset_fail_engine(void *arg)
 out:
 		pr_info("%s(%s): %d resets\n", __func__, engine->name, count);
 skip:
-		clear_bit(I915_RESET_ENGINE + id, &gt->reset.flags);
+		clear_and_wake_up_bit(I915_RESET_ENGINE + id, &gt->reset.flags);
 		st_engine_heartbeat_enable(engine);
 		intel_context_put(ce);
 
@@ -734,7 +736,8 @@ static int __igt_reset_engine(struct intel_gt *gt, bool active)
 		reset_engine_count = i915_reset_engine_count(global, engine);
 
 		st_engine_heartbeat_disable(engine);
-		set_bit(I915_RESET_ENGINE + id, &gt->reset.flags);
+		GEM_BUG_ON(test_and_set_bit(I915_RESET_ENGINE + id,
+					    &gt->reset.flags));
 		count = 0;
 		do {
 			struct i915_request *rq = NULL;
@@ -824,7 +827,7 @@ static int __igt_reset_engine(struct intel_gt *gt, bool active)
 			if (err)
 				break;
 		} while (time_before(jiffies, end_time));
-		clear_bit(I915_RESET_ENGINE + id, &gt->reset.flags);
+		clear_and_wake_up_bit(I915_RESET_ENGINE + id, &gt->reset.flags);
 		st_engine_heartbeat_enable(engine);
 		pr_info("%s: Completed %lu %s resets\n",
 			engine->name, count, active ? "active" : "idle");
@@ -1042,7 +1045,8 @@ static int __igt_reset_engines(struct intel_gt *gt,
 		yield(); /* start all threads before we begin */
 
 		st_engine_heartbeat_disable_no_pm(engine);
-		set_bit(I915_RESET_ENGINE + id, &gt->reset.flags);
+		GEM_BUG_ON(test_and_set_bit(I915_RESET_ENGINE + id,
+					    &gt->reset.flags));
 		do {
 			struct i915_request *rq = NULL;
 			struct intel_selftest_saved_policy saved;
@@ -1165,7 +1169,7 @@ static int __igt_reset_engines(struct intel_gt *gt,
 			if (err)
 				break;
 		} while (time_before(jiffies, end_time));
-		clear_bit(I915_RESET_ENGINE + id, &gt->reset.flags);
+		clear_and_wake_up_bit(I915_RESET_ENGINE + id, &gt->reset.flags);
 		st_engine_heartbeat_enable_no_pm(engine);
 
 		pr_info("i915_reset_engine(%s:%s): %lu resets\n",

drivers/gpu/drm/i915/selftests/igt_reset.c

@@ -36,7 +36,7 @@ void igt_global_reset_unlock(struct intel_gt *gt)
 	enum intel_engine_id id;
 
 	for_each_engine(engine, gt, id)
-		clear_bit(I915_RESET_ENGINE + id, &gt->reset.flags);
+		clear_and_wake_up_bit(I915_RESET_ENGINE + id, &gt->reset.flags);
 
 	clear_bit(I915_RESET_BACKOFF, &gt->reset.flags);
 	wake_up_all(&gt->reset.queue);