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

["wangtao (EQ)" <wangtao554@huawei.com>]

在 2025/9/11 20:53, Greg KH 写道:
> On Thu, Sep 11, 2025 at 08:30:44PM +0800, wangtao (EQ) wrote:
>> 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@huawei.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.
> That is required for us to be able to take a patch into the stable
> trees, thanks.
>
> greg k-h
I have resent this patch for linus's tree.

Please review on the following thread:


Link: 
https://lore.kernel.org/all/20250911124249.1154043-1-wangtao554@huawei.com/


Thanks.