linux-kernel - Re: [PATCH v2 0/6] RCU tasks fixes for v6.9

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Message-ID: <ZdiOot2RJm1VuzSJ@lothringen>
Date: Fri, 23 Feb 2024 13:25:06 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Boqun Feng <boqun.feng@...il.com>, linux-kernel@...r.kernel.org,
	rcu@...r.kernel.org, Neeraj Upadhyay <Neeraj.Upadhyay@....com>
Subject: Re: [PATCH v2 0/6] RCU tasks fixes for v6.9

On Thu, Feb 22, 2024 at 02:09:17PM -0800, Paul E. McKenney wrote:
> On Thu, Feb 22, 2024 at 05:52:23PM +0100, Frederic Weisbecker wrote:
> > Le Fri, Feb 16, 2024 at 05:27:35PM -0800, Boqun Feng a écrit :
> > > Hi,
> > > 
> > > This series contains the fixes of RCU tasks for v6.9. You can also find
> > > the series at:
> > > 
> > > 	git://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git rcu-tasks.2024.02.14a
> > > 
> > > Changes since v1:
> > > 
> > > *	Update with Paul's rework on "Eliminate deadlocks involving
> > > 	do_exit() and RCU task"
> > > 
> > > The detailed list of changes:
> > > 
> > > Paul E. McKenney (6):
> > >   rcu-tasks: Repair RCU Tasks Trace quiescence check
> > >   rcu-tasks: Add data to eliminate RCU-tasks/do_exit() deadlocks
> > >   rcu-tasks: Initialize data to eliminate RCU-tasks/do_exit() deadlocks
> > >   rcu-tasks: Maintain lists to eliminate RCU-tasks/do_exit() deadlocks
> > >   rcu-tasks: Eliminate deadlocks involving do_exit() and RCU tasks
> > 
> > Food for later thoughts and further improvements: would it make sense to
> > call exit_rcu_tasks_start() on fork() instead and rely solely on
> > each CPUs' rtp_exit_list instead of the tasklist?
> 
> It might well.
> 
> One big advantage of doing that is the ability to incrementally traverse
> the tasks.  But is there some good way of doing that to the full task
> lists?  If so, everyone could benefit.

What do you mean by incrementally? You mean being able to cond_resched()
in the middle of the tasks iteration? Yeah not sure that's possible...

Thanks.

> 
> 							Thanx, Paul
> 
> > Thanks.
> > 
> > >   rcu-tasks: Maintain real-time response in rcu_tasks_postscan()
> > > 
> > >  include/linux/rcupdate.h |   4 +-
> > >  include/linux/sched.h    |   2 +
> > >  init/init_task.c         |   1 +
> > >  kernel/fork.c            |   1 +
> > >  kernel/rcu/tasks.h       | 110 ++++++++++++++++++++++++++++++---------
> > >  5 files changed, 90 insertions(+), 28 deletions(-)
> > > 
> > > -- 
> > > 2.43.0
> > > 
> > > 
> >