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SubjectRe: [PATCH] 4.4.86-rt99: fix sync breakage between nr_cpus_allowed and cpus_allowed
On Tue, Nov 21, 2017 at 09:33:52AM -0500, joe.korty@concurrent-rt.com wrote:
> On Mon, Nov 20, 2017 at 11:57:51PM -0500, Steven Rostedt wrote:
> > On Mon, 20 Nov 2017 23:02:07 -0500
> > Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> >
> > > Ideally, I would like to stay close to what upstream -rt does. Would
> > > you be able to backport the 4.11-rt patch?
> > >
> > > I'm currently working on releasing 4.9-rt and 4.4-rt with the latest
> > > backports. I could easily add this one too.
> >
> > Speaking of which. I just backported this patch to 4.4-rt. Is this what
> > you are talking about?
>
> Yes it is.
> Thanks for finding that!
> Joe

I spoke too fast. You will a variant of my one-liner fix
when you backport the 4.11.12-r16 patch:

rt-Increase-decrease-the-nr-of-migratory-tasks-when-.patch

to 4.9-rt and 4.4-rt. The fix of interest is the introduction of

p->nr_cpus_allowed = cpumask_weight(&p->cpus_mask);

to migrate_enable_update_cpus_allowed().

Regards,
Joe

>
> > >From 1dc89be37874bfc7bb4a0ea7c45492d7db39f62b Mon Sep 17 00:00:00 2001
> > From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > Date: Mon, 19 Jun 2017 09:55:47 +0200
> > Subject: [PATCH] sched/migrate disable: handle updated task-mask mg-dis
> > section
> >
> > If task's cpumask changes while in the task is in a migrate_disable()
> > section then we don't react on it after a migrate_enable(). It matters
> > however if current CPU is no longer part of the cpumask. We also miss
> > the ->set_cpus_allowed() callback.
> > This patch fixes it by setting task->migrate_disable_update once we this
> > "delayed" hook.
> > This bug was introduced while fixing unrelated issue in
> > migrate_disable() in v4.4-rt3 (update_migrate_disable() got removed
> > during that).
> >
> > Cc: stable-rt@vger.kernel.org
> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> > ---
> > include/linux/sched.h | 1
> > kernel/sched/core.c | 59 ++++++++++++++++++++++++++++++++++++++++++++------
> > 2 files changed, 54 insertions(+), 6 deletions(-)
> >
> > Index: stable-rt.git/include/linux/sched.h
> > ===================================================================
> > --- stable-rt.git.orig/include/linux/sched.h 2017-11-20 23:43:24.214077537 -0500
> > +++ stable-rt.git/include/linux/sched.h 2017-11-20 23:43:24.154079278 -0500
> > @@ -1438,6 +1438,7 @@ struct task_struct {
> > unsigned int policy;
> > #ifdef CONFIG_PREEMPT_RT_FULL
> > int migrate_disable;
> > + int migrate_disable_update;
> > # ifdef CONFIG_SCHED_DEBUG
> > int migrate_disable_atomic;
> > # endif
> > Index: stable-rt.git/kernel/sched/core.c
> > ===================================================================
> > --- stable-rt.git.orig/kernel/sched/core.c 2017-11-20 23:43:24.214077537 -0500
> > +++ stable-rt.git/kernel/sched/core.c 2017-11-20 23:56:05.071687323 -0500
> > @@ -1212,18 +1212,14 @@ void set_cpus_allowed_common(struct task
> > p->nr_cpus_allowed = cpumask_weight(new_mask);
> > }
> >
> > -void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
> > +static void __do_set_cpus_allowed_tail(struct task_struct *p,
> > + const struct cpumask *new_mask)
> > {
> > struct rq *rq = task_rq(p);
> > bool queued, running;
> >
> > lockdep_assert_held(&p->pi_lock);
> >
> > - if (__migrate_disabled(p)) {
> > - cpumask_copy(&p->cpus_allowed, new_mask);
> > - return;
> > - }
> > -
> > queued = task_on_rq_queued(p);
> > running = task_current(rq, p);
> >
> > @@ -1246,6 +1242,20 @@ void do_set_cpus_allowed(struct task_str
> > enqueue_task(rq, p, ENQUEUE_RESTORE);
> > }
> >
> > +void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
> > +{
> > + if (__migrate_disabled(p)) {
> > + lockdep_assert_held(&p->pi_lock);
> > +
> > + cpumask_copy(&p->cpus_allowed, new_mask);
> > +#if defined(CONFIG_PREEMPT_RT_FULL) && defined(CONFIG_SMP)
> > + p->migrate_disable_update = 1;
> > +#endif
> > + return;
> > + }
> > + __do_set_cpus_allowed_tail(p, new_mask);
> > +}
> > +
> > static DEFINE_PER_CPU(struct cpumask, sched_cpumasks);
> > static DEFINE_MUTEX(sched_down_mutex);
> > static cpumask_t sched_down_cpumask;
> > @@ -3231,6 +3241,43 @@ void migrate_enable(void)
> > */
> > p->migrate_disable = 0;
> >
> > + if (p->migrate_disable_update) {
> > + unsigned long flags;
> > + struct rq *rq;
> > +
> > + rq = task_rq_lock(p, &flags);
> > + update_rq_clock(rq);
> > +
> > + __do_set_cpus_allowed_tail(p, &p->cpus_allowed);
> > + task_rq_unlock(rq, p, &flags);
> > +
> > + p->migrate_disable_update = 0;
> > +
> > + WARN_ON(smp_processor_id() != task_cpu(p));
> > + if (!cpumask_test_cpu(task_cpu(p), &p->cpus_allowed)) {
> > + const struct cpumask *cpu_valid_mask = cpu_active_mask;
> > + struct migration_arg arg;
> > + unsigned int dest_cpu;
> > +
> > + if (p->flags & PF_KTHREAD) {
> > + /*
> > + * Kernel threads are allowed on online && !active CPUs
> > + */
> > + cpu_valid_mask = cpu_online_mask;
> > + }
> > + dest_cpu = cpumask_any_and(cpu_valid_mask, &p->cpus_allowed);
> > + arg.task = p;
> > + arg.dest_cpu = dest_cpu;
> > +
> > + unpin_current_cpu();
> > + preempt_lazy_enable();
> > + preempt_enable();
> > + stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg);
> > + tlb_migrate_finish(p->mm);
> > + return;
> > + }
> > + }
> > +
> > unpin_current_cpu();
> > preempt_enable();
> > preempt_lazy_enable();

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