linux-kernel - Re: [BUG v4.14-rt] kernel BUG at /work/rt/stable-rt.git/kernel/sched/core.c:1639!

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Date:   Wed, 22 Aug 2018 12:33:15 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Mike Galbraith <efault@....de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Julia Cartwright <julia@...com>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [BUG v4.14-rt] kernel BUG at
 /work/rt/stable-rt.git/kernel/sched/core.c:1639!


Sebastian,


On Wed, 22 Aug 2018 12:17:49 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Sun, 19 Aug 2018 08:28:35 +0200
> Mike Galbraith <efault@....de> wrote:
> 
> > On Sat, 2018-08-18 at 15:13 +0200, Mike Galbraith wrote:
> > > seems it has be something from the 4.17 cycle that went back to 4.14-
> > > stable after 4.1[56]-stable trees went extinct.  
> > 
> > See ("sched/core: Require cpu_active() in select_task_rq(), for user tasks")
> > 
> > Fix it like so?
> > 
> > sched: Allow pinned user tasks to be awakened to the CPU they pinned
> > 
> > Since 7af443ee16976, select_fallback_rq() will BUG() if the CPU to
> > which a task has pinned itself and pinned becomes !cpu_active()
> > while it slept.  Serving a 10 megaton eviction notice is neither
> > helpful nor required, the task will migrate when it can do so.
> 
> This seems to fix the issue that I was seeing. Thanks!
> 
> I'll add this to my repo as well.

I'm going to hold off on pulling this in until I see it in your tree,
because a stable RT branch should not carry anything that isn't in the
head RT tree. And it appears that this can affect your repo too.

-- Steve

> 
> > 
> > Signed-off-by: Mike Galbraith <efault@....de>
> > ---
> >  kernel/sched/core.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -980,7 +980,7 @@ static inline bool is_cpu_allowed(struct
> >  	if (!cpumask_test_cpu(cpu, p->cpus_ptr))
> >  		return false;
> >  
> > -	if (is_per_cpu_kthread(p))
> > +	if (is_per_cpu_kthread(p) || __migrate_disabled(p))
> >  		return cpu_online(cpu);
> >  
> >  	return cpu_active(cpu);
>