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

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Message-ID: <0614bb1c-3dc9-4ad1-9135-19662e20163b@huawei.com>
Date: Thu, 11 Sep 2025 20:30:44 +0800
From: "wangtao (EQ)" <wangtao554@...wei.com>
To: Greg KH <gregkh@...uxfoundation.org>
CC: <stable@...r.kernel.org>, <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: Re: [PATCH stable/linux-5.10.y] sched/core: Fix potential deadlock on
 rq lock


在 2025/9/11 20:20, Greg KH 写道:
> On Mon, Sep 08, 2025 at 08:42:30AM +0000, Wang Tao wrote:
>> 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
>>
>>
Sorry, we initially discovered the issue while testing the stable 
branch, and it seems that the mainline has the same problem, but I 
haven't submitted a patch yet.


Thanks

Tao

> What is the git commit id of this in Linus's tree?
>
> thanks,
>
> greg k-h
>