From 00737bebaadaab0c2faa04c5ce5ee788da651a14 Mon Sep 17 00:00:00 2001
From: Wander Lairson Costa <wander@redhat.com>
Date: Wed, 14 Jun 2023 09:23:22 -0300
Subject: [PATCH 57/63] sched: avoid false lockdep splat in put_task_struct()

In put_task_struct(), a spin_lock is indirectly acquired under the kernel
stock. When running the kernel in real-time (RT) configuration, the
operation is dispatched to a preemptible context call to ensure
guaranteed preemption. However, if PROVE_RAW_LOCK_NESTING is enabled
and __put_task_struct() is called while holding a raw_spinlock, lockdep
incorrectly reports an "Invalid lock context" in the stock kernel.

This false splat occurs because lockdep is unaware of the different
route taken under RT. To address this issue, override the inner wait
type to prevent the false lockdep splat.

Signed-off-by: Wander Lairson Costa <wander@redhat.com>
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Luis Goncalves <lgoncalv@redhat.com>
Link: https://lore.kernel.org/r/20230614122323.37957-3-wander@redhat.com
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
(cherry picked from commit a5e446e728e89d5f5c5e427cc919bc7813c64c28)
Signed-off-by: Clark Williams <clark.williams@gmail.com>
---
 include/linux/sched/task.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index aaa25ed1a8fe..a51c36397324 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -141,8 +141,12 @@ static inline void put_task_struct(struct task_struct *t)
 	 */
 	if (IS_ENABLED(CONFIG_PREEMPT_RT) && !preemptible())
 		call_rcu(&t->rcu, __put_task_struct_rcu_cb);
-	else
+	else {
+		static DEFINE_WAIT_OVERRIDE_MAP(put_task_map, LD_WAIT_SLEEP);
+		lock_map_acquire_try(&put_task_map);
 		__put_task_struct(t);
+		lock_map_release(&put_task_map);
+	}
 }
 
 DEFINE_FREE(put_task, struct task_struct *, if (_T) put_task_struct(_T))
-- 
2.46.0

