linux-kernel - [PATCH stable/linux-5.10.y] sched/core: Fix potential deadlock on rq lock

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Message-ID: <20250908084230.848195-1-wangtao554@huawei.com>
Date: Mon, 8 Sep 2025 08:42:30 +0000
From: Wang Tao <wangtao554@...wei.com>
To: <stable@...r.kernel.org>
CC: <mingo@...hat.com>, <peterz@...radead.org>, <juri.lelli@...hat.com>,
	<vincent.guittot@...aro.org>, <dietmar.eggemann@....com>,
	<rostedt@...dmis.org>, <bsegall@...gle.com>, <mgorman@...e.de>,
	<bristot@...hat.com>, <tglx@...utronix.de>, <frederic@...nel.org>,
	<linux-kernel@...r.kernel.org>, <tanghui20@...wei.com>,
	<zhangqiao22@...wei.com>
Subject: [PATCH stable/linux-5.10.y] sched/core: Fix potential deadlock on rq lock

When CPU 1 enters the nohz_full state, and the kworker on CPU 0 executes
the function sched_tick_remote, holding the lock on CPU1's rq
and triggering the warning WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3).
This leads to the process of printing the warning message, where the
console_sem semaphore is held. At this point, the print task on the
CPU1's rq cannot acquire the console_sem and joins the wait queue,
entering the UNINTERRUPTIBLE state. It waits for the console_sem to be
released and then wakes up. After the task on CPU 0 releases
the console_sem, it wakes up the waiting console_sem task.
In try_to_wake_up, it attempts to acquire the lock on CPU1's rq again,
resulting in a deadlock.

The triggering scenario is as follows:

CPU 0								CPU1
sched_tick_remote
WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3)

report_bug							con_write
printk

console_unlock
								do_con_write
								console_lock
								down(&console_sem)
								list_add_tail(&waiter.list, &sem->wait_list);
up(&console_sem)
wake_up_q(&wake_q)
try_to_wake_up
__task_rq_lock
_raw_spin_lock

This patch fixes the issue by deffering all printk console printing
during the lock holding period.

Fixes: d84b31313ef8 ("sched/isolation: Offload residual 1Hz scheduler tick")
Signed-off-by: Wang Tao <wangtao554@...wei.com>
---
 kernel/sched/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 40f40f359c5d..fd2c83058ec2 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4091,6 +4091,7 @@ static void sched_tick_remote(struct work_struct *work)
 		goto out_requeue;

 	rq_lock_irq(rq, &rf);
+	printk_deferred_enter();
 	curr = rq->curr;
 	if (cpu_is_offline(cpu))
 		goto out_unlock;
@@ -4109,6 +4110,7 @@ static void sched_tick_remote(struct work_struct *work)

 	calc_load_nohz_remote(rq);
 out_unlock:
+	printk_deferred_exit();
 	rq_unlock_irq(rq, &rf);
 out_requeue:

-- 
2.34.1