sched: Change the sched_class::set_cpus_allowed() calling context

Change the calling context of sched_class::set_cpus_allowed() such
that we can assume the task is inactive.

This allows us to easily make changes that affect accounting done by
enqueue/dequeue. This does in fact completely remove
set_cpus_allowed_rt() and greatly reduces set_cpus_allowed_dl().

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dedekind1@gmail.com
Cc: juri.lelli@arm.com
Cc: mgorman@suse.de
Cc: riel@redhat.com
Cc: rostedt@goodmis.org
Link: http://lkml.kernel.org/r/20150515154833.667516139@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

3 files changed, 26 insertions, 81 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 740f90bdc67b..9917c962be99 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1163,8 +1163,31 @@ void set_cpus_allowed_common(struct task_struct *p, const struct cpumask *new_ma
 
 void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
 {
+        struct rq *rq = task_rq(p);
+        bool queued, running;
+
         lockdep_assert_held(&p->pi_lock);
+
+        queued = task_on_rq_queued(p);
+        running = task_current(rq, p);
+
+        if (queued) {
+                /*
+                 * Because __kthread_bind() calls this on blocked tasks without
+                 * holding rq->lock.
+                 */
+                lockdep_assert_held(&rq->lock);
+                dequeue_task(rq, p, 0);
+        }
+        if (running)
+                put_prev_task(rq, p);
+
         p->sched_class->set_cpus_allowed(p, new_mask);
+
+        if (running)
+                p->sched_class->set_curr_task(rq);
+        if (queued)
+                enqueue_task(rq, p, 0);
 }
 
 /*
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index dc357fa572b0..b4730565a45d 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1668,9 +1668,8 @@ static void task_woken_dl(struct rq *rq, struct task_struct *p)
 static void set_cpus_allowed_dl(struct task_struct *p,
                                 const struct cpumask *new_mask)
 {
-        struct rq *rq;
         struct root_domain *src_rd;
-        int weight;
+        struct rq *rq;
 
         BUG_ON(!dl_task(p));
 
@@ -1696,41 +1695,7 @@ static void set_cpus_allowed_dl(struct task_struct *p,
                 raw_spin_unlock(&src_dl_b->lock);
         }
 
-        weight = cpumask_weight(new_mask);
-
-        /*
-         * Only update if the process changes its state from whether it
-         * can migrate or not.
-         */
-        if ((p->nr_cpus_allowed > 1) == (weight > 1))
-                goto done;
-
-        /*
-         * Update only if the task is actually running (i.e.,
-         * it is on the rq AND it is not throttled).
-         */
-        if (!on_dl_rq(&p->dl))
-                goto done;
-
-        /*
-         * The process used to be able to migrate OR it can now migrate
-         */
-        if (weight <= 1) {
-                if (!task_current(rq, p))
-                        dequeue_pushable_dl_task(rq, p);
-                BUG_ON(!rq->dl.dl_nr_migratory);
-                rq->dl.dl_nr_migratory--;
-        } else {
-                if (!task_current(rq, p))
-                        enqueue_pushable_dl_task(rq, p);
-                rq->dl.dl_nr_migratory++;
-        }
-
-        update_dl_migration(&rq->dl);
-
-done:
-        cpumask_copy(&p->cpus_allowed, new_mask);
-        p->nr_cpus_allowed = weight;
+        set_cpus_allowed_common(p, new_mask);
 }
 
 /* Assumes rq->lock is held */
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 63692efeca82..d2ea59364a1c 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2076,49 +2076,6 @@ static void task_woken_rt(struct rq *rq, struct task_struct *p)
                 push_rt_tasks(rq);
 }
 
-static void set_cpus_allowed_rt(struct task_struct *p,
-                                const struct cpumask *new_mask)
-{
-        struct rq *rq;
-        int weight;
-
-        BUG_ON(!rt_task(p));
-
-        weight = cpumask_weight(new_mask);
-
-        /*
-         * Only update if the process changes its state from whether it
-         * can migrate or not.
-         */
-        if ((p->nr_cpus_allowed > 1) == (weight > 1))
-                goto done;
-
-        if (!task_on_rq_queued(p))
-                goto done;
-
-        rq = task_rq(p);
-
-        /*
-         * The process used to be able to migrate OR it can now migrate
-         */
-        if (weight <= 1) {
-                if (!task_current(rq, p))
-                        dequeue_pushable_task(rq, p);
-                BUG_ON(!rq->rt.rt_nr_migratory);
-                rq->rt.rt_nr_migratory--;
-        } else {
-                if (!task_current(rq, p))
-                        enqueue_pushable_task(rq, p);
-                rq->rt.rt_nr_migratory++;
-        }
-
-        update_rt_migration(&rq->rt);
-
-done:
-        cpumask_copy(&p->cpus_allowed, new_mask);
-        p->nr_cpus_allowed = weight;
-}
-
 /* Assumes rq->lock is held */
 static void rq_online_rt(struct rq *rq)
 {
@@ -2327,7 +2284,7 @@ const struct sched_class rt_sched_class = {
 #ifdef CONFIG_SMP
         .select_task_rq         = select_task_rq_rt,
 
-        .set_cpus_allowed       = set_cpus_allowed_rt,
+        .set_cpus_allowed       = set_cpus_allowed_common,
         .rq_online              = rq_online_rt,
         .rq_offline             = rq_offline_rt,
         .task_woken             = task_woken_rt,