linux-kernel - Re: [PATCH] rcu-tasks: Fix the comments for tasks_rcu_exit_srcu_stall

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Message-ID: <CALm+0cWESKy4xCg9Eg4-6OoxPcQ102F4TY5C80jgugrmM3ptFA@mail.gmail.com>
Date: Tue, 27 Feb 2024 14:08:00 +0800
From: Z qiang <qiang.zhang1211@...il.com>
To: paulmck@...nel.org
Cc: frederic@...nel.org, neeraj.upadhyay@...nel.org, joel@...lfernandes.org, 
	rcu@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu-tasks: Fix the comments for tasks_rcu_exit_srcu_stall_timer

>
> On Mon, Feb 26, 2024 at 11:28:57AM +0800, Z qiang wrote:
> > >
> > > The synchronize_srcu() has been removed by commit("rcu-tasks: Eliminate
> > > deadlocks involving do_exit() and RCU tasks") in rcu_tasks_postscan.
> > > This commit therefore fix the comments of tasks_rcu_exit_srcu_stall_timer.
> > >
> > > Signed-off-by: Zqiang <qiang.zhang1211@...il.com>
> > > ---
> > >  kernel/rcu/tasks.h | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> > > index 78d74c81cc24..d5319bbe8c98 100644
> > > --- a/kernel/rcu/tasks.h
> > > +++ b/kernel/rcu/tasks.h
> > > @@ -150,7 +150,7 @@ static struct rcu_tasks rt_name =                                                   \
> > >
> > >  #ifdef CONFIG_TASKS_RCU
> > >
> > > -/* Report delay in synchronize_srcu() completion in rcu_tasks_postscan(). */
> > > +/* Report delay of scan exiting tasklist in rcu_tasks_postscan(). */
> > >  static void tasks_rcu_exit_srcu_stall(struct timer_list *unused);
> > >  static DEFINE_TIMER(tasks_rcu_exit_srcu_stall_timer, tasks_rcu_exit_srcu_stall);
> >
> > Is this timer not necessary? any thoughts?
>
> We have preemption points in the list traversals, and things like mutex
> contention on the do_exit() path could result in extremely long lists,
> so I believe we do need the timer.
>
> But what did you have in mind?

Thanks for the explanation,  I ignored the scenario where the
lists might be very long :)

Thanks
Zqiang

>
>                                                         Thanx, Paul
>
> > Thanks
> > Zqiang
> >
> >
> > >  #endif
> > > --
> > > 2.17.1
> > >