sched/fair: Fix and optimize the fork() path

[cascardo/linux.git] / kernel / sched / core.c

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e406ba0..fa3434d 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2383,9 +2383,6 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
                p->sched_class = &fair_sched_class;
        }
 
-       if (p->sched_class->task_fork)
-               p->sched_class->task_fork(p);
-
        /*
         * The child is not yet in the pid-hash so no cgroup attach races,
         * and the cgroup is pinned to this child due to cgroup_fork()
@@ -2394,7 +2391,13 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
         * Silence PROVE_RCU.
         */
        raw_spin_lock_irqsave(&p->pi_lock, flags);
-       set_task_cpu(p, cpu);
+       /*
+        * We're setting the cpu for the first time, we don't migrate,
+        * so use __set_task_cpu().
+        */
+       __set_task_cpu(p, cpu);
+       if (p->sched_class->task_fork)
+               p->sched_class->task_fork(p);
        raw_spin_unlock_irqrestore(&p->pi_lock, flags);
 
 #ifdef CONFIG_SCHED_INFO
@@ -2534,8 +2537,11 @@ void wake_up_new_task(struct task_struct *p)
         * Fork balancing, do it here and not earlier because:
         *  - cpus_allowed can change in the fork path
         *  - any previously selected cpu might disappear through hotplug
+        *
+        * Use __set_task_cpu() to avoid calling sched_class::migrate_task_rq,
+        * as we're not fully set-up yet.
         */
-       set_task_cpu(p, select_task_rq(p, task_cpu(p), SD_BALANCE_FORK, 0));
+       __set_task_cpu(p, select_task_rq(p, task_cpu(p), SD_BALANCE_FORK, 0));
 #endif
        rq = __task_rq_lock(p, &rf);
        post_init_entity_util_avg(&p->se);