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

-- Steve

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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