[Intel-gfx] [PATCH 14/27] drm/i915/guc: Don't touch guc_state.sched_state without a lock

[Matthew Brost]

Before we did some clever tricks to not use the a lock when touching
guc_state.sched_state in certain cases. Don't do that, enforce the use
of the lock.

Part of this is removing a dead code path from guc_lrc_desc_pin where a
context could be deregistered when the aforementioned function was
called from the submission path. Remove this dead code and add a
GEM_BUG_ON if this path is ever attempted to be used.

v2:
 (kernel test robo )
  - Add __maybe_unused to sched_state_is_init()

Signed-off-by: Matthew Brost <matthew.brost at intel.com>
Reported-by: kernel test robot <lkp at intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
---
 .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 58 ++++++++++---------
 1 file changed, 32 insertions(+), 26 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
index 1cb97e98871c..901d867a4d90 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
@@ -151,11 +151,23 @@ static inline void clr_context_registered(struct intel_context *ce)
 
 static inline void init_sched_state(struct intel_context *ce)
 {
-	/* Only should be called from guc_lrc_desc_pin() */
+	lockdep_assert_held(&ce->guc_state.lock);
 	atomic_set(&ce->guc_sched_state_no_lock, 0);
 	ce->guc_state.sched_state &= SCHED_STATE_BLOCKED_MASK;
 }
 
+__maybe_unused
+static bool sched_state_is_init(struct intel_context *ce)
+{
+	/*
+	 * XXX: Kernel contexts can have SCHED_STATE_NO_LOCK_REGISTERED after
+	 * suspend.
+	 */
+	return !(atomic_read(&ce->guc_sched_state_no_lock) &
+		 ~SCHED_STATE_NO_LOCK_REGISTERED) &&
+		!(ce->guc_state.sched_state &= ~SCHED_STATE_BLOCKED_MASK);
+}
+
 static inline bool
 context_wait_for_deregister_to_register(struct intel_context *ce)
 {
@@ -166,7 +178,7 @@ context_wait_for_deregister_to_register(struct intel_context *ce)
 static inline void
 set_context_wait_for_deregister_to_register(struct intel_context *ce)
 {
-	/* Only should be called from guc_lrc_desc_pin() without lock */
+	lockdep_assert_held(&ce->guc_state.lock);
 	ce->guc_state.sched_state |=
 		SCHED_STATE_WAIT_FOR_DEREGISTER_TO_REGISTER;
 }
@@ -605,9 +617,7 @@ static void scrub_guc_desc_for_outstanding_g2h(struct intel_guc *guc)
 	bool pending_disable, pending_enable, deregister, destroyed, banned;
 
 	xa_for_each(&guc->context_lookup, index, ce) {
-		/* Flush context */
 		spin_lock_irqsave(&ce->guc_state.lock, flags);
-		spin_unlock_irqrestore(&ce->guc_state.lock, flags);
 
 		/*
 		 * Once we are at this point submission_disabled() is guaranteed
@@ -623,6 +633,8 @@ static void scrub_guc_desc_for_outstanding_g2h(struct intel_guc *guc)
 		banned = context_banned(ce);
 		init_sched_state(ce);
 
+		spin_unlock_irqrestore(&ce->guc_state.lock, flags);
+
 		if (pending_enable || destroyed || deregister) {
 			decr_outstanding_submission_g2h(guc);
 			if (deregister)
@@ -1323,6 +1335,7 @@ static int guc_lrc_desc_pin(struct intel_context *ce, bool loop)
 	int ret = 0;
 
 	GEM_BUG_ON(!engine->mask);
+	GEM_BUG_ON(!sched_state_is_init(ce));
 
 	/*
 	 * Ensure LRC + CT vmas are is same region as write barrier is done
@@ -1351,7 +1364,6 @@ static int guc_lrc_desc_pin(struct intel_context *ce, bool loop)
 	desc->priority = ce->guc_prio;
 	desc->context_flags = CONTEXT_REGISTRATION_FLAG_KMD;
 	guc_context_policy_init(engine, desc);
-	init_sched_state(ce);
 
 	/*
 	 * The context_lookup xarray is used to determine if the hardware
@@ -1362,26 +1374,23 @@ static int guc_lrc_desc_pin(struct intel_context *ce, bool loop)
 	 * registering this context.
 	 */
 	if (context_registered) {
+		bool disabled;
+		unsigned long flags;
+
 		trace_intel_context_steal_guc_id(ce);
-		if (!loop) {
+		GEM_BUG_ON(!loop);
+
+		/* Seal race with Reset */
+		spin_lock_irqsave(&ce->guc_state.lock, flags);
+		disabled = submission_disabled(guc);
+		if (likely(!disabled)) {
 			set_context_wait_for_deregister_to_register(ce);
 			intel_context_get(ce);
-		} else {
-			bool disabled;
-			unsigned long flags;
-
-			/* Seal race with Reset */
-			spin_lock_irqsave(&ce->guc_state.lock, flags);
-			disabled = submission_disabled(guc);
-			if (likely(!disabled)) {
-				set_context_wait_for_deregister_to_register(ce);
-				intel_context_get(ce);
-			}
-			spin_unlock_irqrestore(&ce->guc_state.lock, flags);
-			if (unlikely(disabled)) {
-				reset_lrc_desc(guc, desc_idx);
-				return 0;	/* Will get registered later */
-			}
+		}
+		spin_unlock_irqrestore(&ce->guc_state.lock, flags);
+		if (unlikely(disabled)) {
+			reset_lrc_desc(guc, desc_idx);
+			return 0;	/* Will get registered later */
 		}
 
 		/*
@@ -1390,10 +1399,7 @@ static int guc_lrc_desc_pin(struct intel_context *ce, bool loop)
 		 */
 		with_intel_runtime_pm(runtime_pm, wakeref)
 			ret = deregister_context(ce, ce->guc_id, loop);
-		if (unlikely(ret == -EBUSY)) {
-			clr_context_wait_for_deregister_to_register(ce);
-			intel_context_put(ce);
-		} else if (unlikely(ret == -ENODEV)) {
+		if (unlikely(ret == -ENODEV)) {
 			ret = 0;	/* Will get registered later */
 		}
 	} else {
-- 
2.32.0