sched: Remove get_online_cpus() usage

[~andy/linux] / kernel / sched / core.c

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a972acd468b0838e2d08a4103db2c7e5476a2d6c..c06b8d345faef1bd3b796e309190250d75820fdb 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1085,8 +1085,6 @@ int migrate_swap(struct task_struct *cur, struct task_struct *p)
        struct migration_swap_arg arg;
        int ret = -EINVAL;
 
-       get_online_cpus();
-
        arg = (struct migration_swap_arg){
                .src_task = cur,
                .src_cpu = task_cpu(cur),
@@ -1097,6 +1095,10 @@ int migrate_swap(struct task_struct *cur, struct task_struct *p)
        if (arg.src_cpu == arg.dst_cpu)
                goto out;
 
+       /*
+        * These three tests are all lockless; this is OK since all of them
+        * will be re-checked with proper locks held further down the line.
+        */
        if (!cpu_active(arg.src_cpu) || !cpu_active(arg.dst_cpu))
                goto out;
 
@@ -1109,7 +1111,6 @@ int migrate_swap(struct task_struct *cur, struct task_struct *p)
        ret = stop_two_cpus(arg.dst_cpu, arg.src_cpu, migrate_swap_stop, &arg);
 
 out:
-       put_online_cpus();
        return ret;
 }
 
@@ -3710,7 +3711,6 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
        struct task_struct *p;
        int retval;
 
-       get_online_cpus();
        rcu_read_lock();
 
        p = find_process_by_pid(pid);
@@ -3773,7 +3773,6 @@ out_free_cpus_allowed:
        free_cpumask_var(cpus_allowed);
 out_put_task:
        put_task_struct(p);
-       put_online_cpus();
        return retval;
 }
 
@@ -3818,7 +3817,6 @@ long sched_getaffinity(pid_t pid, struct cpumask *mask)
        unsigned long flags;
        int retval;
 
-       get_online_cpus();
        rcu_read_lock();
 
        retval = -ESRCH;
@@ -3831,12 +3829,11 @@ long sched_getaffinity(pid_t pid, struct cpumask *mask)
                goto out_unlock;
 
        raw_spin_lock_irqsave(&p->pi_lock, flags);
-       cpumask_and(mask, &p->cpus_allowed, cpu_online_mask);
+       cpumask_and(mask, &p->cpus_allowed, cpu_active_mask);
        raw_spin_unlock_irqrestore(&p->pi_lock, flags);
 
 out_unlock:
        rcu_read_unlock();
-       put_online_cpus();
 
        return retval;
 }
@@ -6494,14 +6491,17 @@ void __init sched_init_smp(void)
 
        sched_init_numa();
 
-       get_online_cpus();
+       /*
+        * There's no userspace yet to cause hotplug operations; hence all the
+        * cpu masks are stable and all blatant races in the below code cannot
+        * happen.
+        */
        mutex_lock(&sched_domains_mutex);
        init_sched_domains(cpu_active_mask);
        cpumask_andnot(non_isolated_cpus, cpu_possible_mask, cpu_isolated_map);
        if (cpumask_empty(non_isolated_cpus))
                cpumask_set_cpu(smp_processor_id(), non_isolated_cpus);
        mutex_unlock(&sched_domains_mutex);
-       put_online_cpus();
 
        hotcpu_notifier(sched_domains_numa_masks_update, CPU_PRI_SCHED_ACTIVE);
        hotcpu_notifier(cpuset_cpu_active, CPU_PRI_CPUSET_ACTIVE);