[PATCH] sched: force /sbin/init off isolated cpus

Force /sbin/init off isolated cpus (unless every CPU is specified as an
isolcpu).

Users seem to think that the isolated CPUs shouldn't have much running on
them to begin with.  That's fair enough: intuitive, I guess.  It also means
that the cpu affinity masks of tasks will not include isolcpus by default,
which is also more intuitive, perhaps.

/sbin/init is spawned from the boot CPU's idle thread, and /sbin/init
starts the rest of userspace. So if the boot CPU is specified to be an
isolcpu, then prior to this patch, all of userspace will be run there.

(throw in a couple of plausible devinit -> cpuinit conversions I spotted
while we're here).

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Dimitri Sivanich <sivanich@sgi.com>
Acked-by: Paul Jackson <pj@sgi.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/sched.c

@@ -4817,7 +4817,7 @@ void show_state(void)
  * NOTE: this function does not set the idle thread's NEED_RESCHED
  * flag, to make booting more robust.
  */
-void __devinit init_idle(struct task_struct *idle, int cpu)
+void __cpuinit init_idle(struct task_struct *idle, int cpu)
 {
 	struct rq *rq = cpu_rq(cpu);
 	unsigned long flags;
@@ -5461,7 +5461,7 @@ static void cpu_attach_domain(struct sched_domain *sd, int cpu)
 }
 
 /* cpus with isolated domains */
-static cpumask_t __devinitdata cpu_isolated_map = CPU_MASK_NONE;
+static cpumask_t __cpuinitdata cpu_isolated_map = CPU_MASK_NONE;
 
 /* Setup the mask of cpus configured for isolated domains */
 static int __init isolated_cpu_setup(char *str)
@@ -6747,11 +6747,20 @@ static int update_sched_domains(struct notifier_block *nfb,
 
 void __init sched_init_smp(void)
 {
+	cpumask_t non_isolated_cpus;
+
 	lock_cpu_hotplug();
 	arch_init_sched_domains(&cpu_online_map);
+	cpus_andnot(non_isolated_cpus, cpu_online_map, cpu_isolated_map);
+	if (cpus_empty(non_isolated_cpus))
+		cpu_set(smp_processor_id(), non_isolated_cpus);
 	unlock_cpu_hotplug();
 	/* XXX: Theoretical race here - CPU may be hotplugged now */
 	hotcpu_notifier(update_sched_domains, 0);
+
+	/* Move init over to a non-isolated CPU */
+	if (set_cpus_allowed(current, non_isolated_cpus) < 0)
+		BUG();
 }
 #else
 void __init sched_init_smp(void)