linux-kernel - Re: [patch-rt] hotplug, hrtimer: Migrate expired/deferred timers during cpu offline

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Date:   Mon, 14 Aug 2017 09:59:48 +0200
From:   Mike Galbraith <efault@....de>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [patch-rt] hotplug, hrtimer: Migrate expired/deferred timers
 during cpu offline

On Fri, 2017-08-11 at 10:15 +0200, Mike Galbraith wrote:
> On Fri, 2017-08-11 at 09:55 +0200, Mike Galbraith wrote:
> > The below fixes the list debug explosion up.
> > 
> > If we do not migrate expired/deferred timers during cpu offline, ->cb_entry
> > will be corrupted by online initialization of base->expired, leading to a
> > loud list debug complaint should someone call __remove_hrtimer() thereafter.
> > 
> > Signed-off-by: Mike Galvraith <efault@....de>
> ahem.....................b

(actually, I shouldn't have signed, question being why we now leave
them lying about when we _apparently_ previously did not)

> > ---
> >  kernel/time/hrtimer.c |   13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > --- a/kernel/time/hrtimer.c
> > +++ b/kernel/time/hrtimer.c
> > @@ -1802,6 +1802,19 @@ static void migrate_hrtimer_list(struct
> >  		 */
> >  		enqueue_hrtimer(timer, new_base);
> >  	}
> > +
> > +	/*
> > +	 * Finally, migrate any expired timers deferred by RT.
> > +	 */
> > +	while (!list_empty(&old_base->expired)) {
> > +		struct list_head *entry = old_base->expired.next;
> > +
> > +		timer = container_of(entry, struct hrtimer, cb_entry);

(oops, forgot to change that back too. [scribble scribble])

> > +		/* XXX: hm, perhaps defer again instead of enqueueing. */
> > +		__remove_hrtimer(timer, old_base, HRTIMER_STATE_ENQUEUED, 0);
> > +		timer->base = new_base;
> > +		enqueue_hrtimer(timer, new_base);
> > +	}
> >  }
> >  
> >  int hrtimers_dead_cpu(unsigned int scpu)