[PATCH v2] drm/xe/guc: Fix race around q->guc->suspend_pending access

q->guc->suspend_pending is accessed without any common lock.
__suspend_fence_signal(), called from guc_exec_queue_kill() and the
suspend-timeout ban path, clears the flag asynchronously. Meanwhile
handle_sched_done(), guc_exec_queue_stop() and
__guc_exec_queue_process_msg_suspend() check the flag and then call
suspend_fence_signal(), which asserts that it is still set.

As the check and suspend_fence_signal() are not atomic, the clear can
land in between and trip the xe_gt_assert(q->guc->suspend_pending).

The flag is already set and read under the per-queue msg_lock
(xe_sched_msg_lock()) on the suspend and resume paths. Extend that same
lock to the clear paths (kill and ban) and to the three check-then-act
sites so the check and the signal are atomic with respect to the clear.
In __guc_exec_queue_process_msg_suspend() only the non-sleeping branch is
wrapped, since the other branch waits. In handle_sched_done() the flag is
snapshotted under the lock and deregister_exec_queue() is kept outside it.

v2: Document that sched->msg_lock also protects
    guc->suspend_pending, which indicates a suspend message is in
    flight, in addition to the sched->msgs list (Niranjana)

Signed-off-by: Jagmeet Randhawa <[email protected]>
---
 drivers/gpu/drm/xe/xe_gpu_scheduler_types.h  |  5 +++-
 drivers/gpu/drm/xe/xe_guc_exec_queue_types.h |  5 +++-
 drivers/gpu/drm/xe/xe_guc_submit.c           | 29 ++++++++++++++++----
 3 files changed, 32 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_gpu_scheduler_types.h b/drivers/gpu/drm/xe/xe_gpu_scheduler_types.h
index 63d9bf92583c..78ef2e8ded4f 100644
--- a/drivers/gpu/drm/xe/xe_gpu_scheduler_types.h
+++ b/drivers/gpu/drm/xe/xe_gpu_scheduler_types.h
@@ -47,7 +47,10 @@ struct xe_gpu_scheduler {
 	const struct xe_sched_backend_ops	*ops;
 	/** @msgs: list of messages to be processed in @work_process_msg */
 	struct list_head			msgs;
-	/** @msg_lock: Message lock */
+	/**
+	 * @msg_lock: Protects @msgs and guc->suspend_pending (indicates a
+	 * suspend message is in flight) of exec queues on this scheduler.
+	 */
 	spinlock_t				msg_lock;
 	/** @work_process_msg: processes messages */
 	struct work_struct		work_process_msg;
diff --git a/drivers/gpu/drm/xe/xe_guc_exec_queue_types.h b/drivers/gpu/drm/xe/xe_guc_exec_queue_types.h
index d27826b36649..74b711abe257 100644
--- a/drivers/gpu/drm/xe/xe_guc_exec_queue_types.h
+++ b/drivers/gpu/drm/xe/xe_guc_exec_queue_types.h
@@ -52,7 +52,10 @@ struct xe_guc_exec_queue {
 	u16 id;
 	/** @suspend_wait: wait queue used to wait on pending suspends */
 	wait_queue_head_t suspend_wait;
-	/** @suspend_pending: a suspend of the exec_queue is pending */
+	/**
+	 * @suspend_pending: a suspend of the exec_queue is pending.
+	 * Protected by @sched.msg_lock.
+	 */
 	bool suspend_pending;
 	/**
 	 * @suspend_count: Reference count of active suspend requests. The
diff --git a/drivers/gpu/drm/xe/xe_guc_submit.c b/drivers/gpu/drm/xe/xe_guc_submit.c
index 9036f89dff7d..c565c1d32d3a 100644
--- a/drivers/gpu/drm/xe/xe_guc_submit.c
+++ b/drivers/gpu/drm/xe/xe_guc_submit.c
@@ -1928,9 +1928,13 @@ static void __guc_exec_queue_process_msg_suspend(struct xe_sched_msg *msg)
 			set_exec_queue_suspended(q);
 			disable_scheduling(q, false);
 		}
-	} else if (q->guc->suspend_pending) {
-		set_exec_queue_suspended(q);
-		suspend_fence_signal(q);
+	} else {
+		xe_sched_msg_lock(&q->guc->sched);
+		if (q->guc->suspend_pending) {
+			set_exec_queue_suspended(q);
+			suspend_fence_signal(q);
+		}
+		xe_sched_msg_unlock(&q->guc->sched);
 	}
 }
 
@@ -2130,7 +2134,9 @@ static void guc_exec_queue_kill(struct xe_exec_queue *q)
 {
 	trace_xe_exec_queue_kill(q);
 	set_exec_queue_killed(q);
+	xe_sched_msg_lock(&q->guc->sched);
 	__suspend_fence_signal(q);
+	xe_sched_msg_unlock(&q->guc->sched);
 	xe_guc_exec_queue_trigger_cleanup(q);
 }
 
@@ -2392,11 +2398,15 @@ static void guc_exec_queue_suspend_timeout_ban(struct xe_exec_queue *q)
 	 */
 	if (xe_exec_queue_is_multi_queue(q)) {
 		set_exec_queue_group_banned(q);
+		xe_sched_msg_lock(&q->guc->sched);
 		__suspend_fence_signal(q);
+		xe_sched_msg_unlock(&q->guc->sched);
 		xe_guc_exec_queue_group_trigger_cleanup(q);
 	} else {
 		set_exec_queue_banned(q);
+		xe_sched_msg_lock(&q->guc->sched);
 		__suspend_fence_signal(q);
+		xe_sched_msg_unlock(&q->guc->sched);
 		xe_guc_exec_queue_trigger_cleanup(q);
 	}
 }
@@ -2614,10 +2624,12 @@ static void guc_exec_queue_stop(struct xe_guc *guc, struct xe_exec_queue *q)
 		if (exec_queue_destroyed(q))
 			do_destroy = true;
 	}
+	xe_sched_msg_lock(sched);
 	if (q->guc->suspend_pending) {
 		set_exec_queue_suspended(q);
 		suspend_fence_signal(q);
 	}
+	xe_sched_msg_unlock(sched);
 	atomic_and(EXEC_QUEUE_STATE_WEDGED | EXEC_QUEUE_STATE_BANNED |
 		   EXEC_QUEUE_STATE_KILLED | EXEC_QUEUE_STATE_DESTROYED |
 		   EXEC_QUEUE_STATE_SUSPENDED,
@@ -3222,13 +3234,20 @@ static void handle_sched_done(struct xe_guc *guc, struct xe_exec_queue *q,
 		smp_wmb();
 		wake_up_all(&guc->ct.wq);
 	} else {
+		bool was_pending;
+
 		xe_gt_assert(guc_to_gt(guc), runnable_state == 0);
 		xe_gt_assert(guc_to_gt(guc), exec_queue_pending_disable(q));
 
-		if (q->guc->suspend_pending) {
+		xe_sched_msg_lock(&q->guc->sched);
+		was_pending = q->guc->suspend_pending;
+		if (was_pending) {
 			clear_exec_queue_pending_disable(q);
 			suspend_fence_signal(q);
-		} else {
+		}
+		xe_sched_msg_unlock(&q->guc->sched);
+
+		if (!was_pending) {
 			if (exec_queue_banned(q)) {
 				smp_wmb();
 				wake_up_all(&guc->ct.wq);
-- 
2.53.0