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Subject[PATCH 2/2] sched, cpuset: introduce do_set_cpus_allowed() helper function
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Now, we have five task->cpus_allowed writer.

1) sched_rt.c: set_cpus_allowed_rt()
2) sched.c: set_cpus_allowed_ptr()
3) sched.c: init_idle()
4) kthread.c kthread_bind()
5) cpuset.c: cpuset_cpus_allowed_fallback()

And, now (3), (4), (5) don't check p->sched_class->set_cpus_allowed.
It's ok, We have a implicit gurantee that it's safe. However they
theorically slightly bad habit. If any scheduler class will add to
implement ->set_cpus_allowed in future, they may not work.

Then, it would be nice to make good helper function and cleanup.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
---
include/linux/cpuset.h | 3 +--
include/linux/sched.h | 7 +++++++
kernel/cpuset.c | 5 ++---
kernel/kthread.c | 4 ++--
kernel/sched.c | 19 ++++++++++++-------
5 files changed, 24 insertions(+), 14 deletions(-)
diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 42dcbdc..e9eaec5 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -146,8 +146,7 @@ static inline void cpuset_cpus_allowed(struct task_struct *p,

static inline int cpuset_cpus_allowed_fallback(struct task_struct *p)
{
- cpumask_copy(&p->cpus_allowed, cpu_possible_mask);
- p->rt.nr_cpus_allowed = cpumask_weight(&p->cpus_allowed);
+ do_set_cpus_allowed(p, cpu_possible_mask);
return cpumask_any(cpu_active_mask);
}

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 3f7d3f9..fc7964d 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1823,9 +1823,16 @@ static inline void rcu_copy_process(struct task_struct *p)
#endif

#ifdef CONFIG_SMP
+extern void do_set_cpus_allowed(struct task_struct *p,
+ const struct cpumask *new_mask);
+
extern int set_cpus_allowed_ptr(struct task_struct *p,
const struct cpumask *new_mask);
#else
+static inline void do_set_cpus_allowed(struct task_struct *p,
+ const struct cpumask *new_mask)
+{
+}
static inline int set_cpus_allowed_ptr(struct task_struct *p,
const struct cpumask *new_mask)
{
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 6e5bbe8..9c9b754 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2190,7 +2190,7 @@ int cpuset_cpus_allowed_fallback(struct task_struct *tsk)
rcu_read_lock();
cs = task_cs(tsk);
if (cs)
- cpumask_copy(&tsk->cpus_allowed, cs->cpus_allowed);
+ do_set_cpus_allowed(tsk, cs->cpus_allowed);
rcu_read_unlock();

/*
@@ -2217,10 +2217,9 @@ int cpuset_cpus_allowed_fallback(struct task_struct *tsk)
* Like above we can temporary set any mask and rely on
* set_cpus_allowed_ptr() as synchronization point.
*/
- cpumask_copy(&tsk->cpus_allowed, cpu_possible_mask);
+ do_set_cpus_allowed(tsk, cpu_possible_mask);
cpu = cpumask_any(cpu_active_mask);
}
- tsk->rt.nr_cpus_allowed = cpumask_weight(&tsk->cpus_allowed);

return cpu;
}
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 3b34d27..4ba7ccc 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -202,8 +202,8 @@ void kthread_bind(struct task_struct *p, unsigned int cpu)
return;
}

- p->cpus_allowed = cpumask_of_cpu(cpu);
- p->rt.nr_cpus_allowed = 1;
+ /* It's safe because the task is inactive. */
+ do_set_cpus_allowed(p, cpumask_of(cpu));
p->flags |= PF_THREAD_BOUND;
}
EXPORT_SYMBOL(kthread_bind);
diff --git a/kernel/sched.c b/kernel/sched.c
index bfcd219..7867e47 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5819,7 +5819,7 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu)
idle->state = TASK_RUNNING;
idle->se.exec_start = sched_clock();

- cpumask_copy(&idle->cpus_allowed, cpumask_of(cpu));
+ do_set_cpus_allowed(idle, cpumask_of(cpu));
/*
* We're having a chicken and egg problem, even though we are
* holding rq->lock, the cpu isn't yet set to this cpu so the
@@ -5910,6 +5910,16 @@ static inline void sched_init_granularity(void)
}

#ifdef CONFIG_SMP
+void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
+{
+ if (p->sched_class && p->sched_class->set_cpus_allowed)
+ p->sched_class->set_cpus_allowed(p, new_mask);
+ else {
+ cpumask_copy(&p->cpus_allowed, new_mask);
+ p->rt.nr_cpus_allowed = cpumask_weight(new_mask);
+ }
+}
+
/*
* This is how migration works:
*
@@ -5953,12 +5963,7 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
goto out;
}

- if (p->sched_class->set_cpus_allowed)
- p->sched_class->set_cpus_allowed(p, new_mask);
- else {
- cpumask_copy(&p->cpus_allowed, new_mask);
- p->rt.nr_cpus_allowed = cpumask_weight(new_mask);
- }
+ do_set_cpus_allowed(p, new_mask);

/* Can the task run on the task's current CPU? If so, we're done */
if (cpumask_test_cpu(task_cpu(p), new_mask))
--
1.7.3.1




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