linux-kernel - [PATCH 1/6] sched: Constrain locks in sched_submit

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Message-ID: <20230815111430.154558666@infradead.org>
Date:   Tue, 15 Aug 2023 13:01:22 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     bigeasy@...utronix.de, tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        bsegall@...gle.com, boqun.feng@...il.com, swood@...hat.com,
        bristot@...hat.com, dietmar.eggemann@....com, mingo@...hat.com,
        jstultz@...gle.com, juri.lelli@...hat.com, mgorman@...e.de,
        rostedt@...dmis.org, vschneid@...hat.com,
        vincent.guittot@...aro.org, longman@...hat.com, will@...nel.org
Subject: [PATCH 1/6] sched: Constrain locks in sched_submit_work()

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@...radead.org>
---
 kernel/sched/core.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6737,11 +6737,18 @@ 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
@@ -6766,6 +6773,8 @@ 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)