From: Peter Zijlstra <peterz@infradead.org>
Date: Fri, 8 Sep 2023 18:22:48 +0200
Subject: [PATCH 1/7] sched: Constrain locks in sched_submit_work()
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz

Even though sched_submit_work() is ran from preemptible context,
it is discouraged to have it use blocking locks due to the recursion
potential.

Enforce this.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20230908162254.999499-2-bigeasy@linutronix.de
---
 kernel/sched/core.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6721,11 +6721,18 @@ void __noreturn do_task_dead(void)
 
 static inline void sched_submit_work(struct task_struct *tsk)
 {
+	static DEFINE_WAIT_OVERRIDE_MAP(sched_map, LD_WAIT_CONFIG);
 	unsigned int task_flags;
 
 	if (task_is_running(tsk))
 		return;
 
+	/*
+	 * Establish LD_WAIT_CONFIG context to ensure none of the code called
+	 * will use a blocking primitive -- which would lead to recursion.
+	 */
+	lock_map_acquire_try(&sched_map);
+
 	task_flags = tsk->flags;
 	/*
 	 * If a worker goes to sleep, notify and ask workqueue whether it
@@ -6750,6 +6757,8 @@ static inline void sched_submit_work(str
 	 * make sure to submit it to avoid deadlocks.
 	 */
 	blk_flush_plug(tsk->plug, true);
+
+	lock_map_release(&sched_map);
 }
 
 static void sched_update_worker(struct task_struct *tsk)
