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

[wangtao (EQ)]

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@xxxxxxxxxx>
> > > > ---
> > > >    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@xxxxxxxxxx/


Thanks.