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SubjectRe: [PATCH] 4.4.86-rt99: fix sync breakage between nr_cpus_allowed and cpus_allowed
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

> >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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