cpu hotplug: adjust root-domain->online span in response to hotplug event

We currently set the root-domain online span automatically when the
domain is added to the cpu if the cpu is already a member of
cpu_online_map.

This was done as a hack/bug-fix for s2ram, but it also causes a problem
with hotplug CPU_DOWN transitioning.  The right way to fix the original
problem is to actually respond to CPU_UP events, instead of CPU_ONLINE,
which is already too late.

This solves the hung reboot regression reported by Andrew Morton and
others.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 11 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 52b98675acb2..b02e4fc25645 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5813,6 +5813,13 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
                 /* Must be high prio: stop_machine expects to yield to it. */
                 rq = task_rq_lock(p, &flags);
                 __setscheduler(rq, p, SCHED_FIFO, MAX_RT_PRIO-1);
+
+                /* Update our root-domain */
+                if (rq->rd) {
+                        BUG_ON(!cpu_isset(cpu, rq->rd->span));
+                        cpu_set(cpu, rq->rd->online);
+                }
+
                 task_rq_unlock(rq, &flags);
                 cpu_rq(cpu)->migration_thread = p;
                 break;
@@ -5821,15 +5828,6 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
         case CPU_ONLINE_FROZEN:
                 /* Strictly unnecessary, as first user will wake it. */
                 wake_up_process(cpu_rq(cpu)->migration_thread);
-
-                /* Update our root-domain */
-                rq = cpu_rq(cpu);
-                spin_lock_irqsave(&rq->lock, flags);
-                if (rq->rd) {
-                        BUG_ON(!cpu_isset(cpu, rq->rd->span));
-                        cpu_set(cpu, rq->rd->online);
-                }
-                spin_unlock_irqrestore(&rq->lock, flags);
                 break;
 
 #ifdef CONFIG_HOTPLUG_CPU
@@ -6105,8 +6103,6 @@ static void rq_attach_root(struct rq *rq, struct root_domain *rd)
         rq->rd = rd;
 
         cpu_set(rq->cpu, rd->span);
-        if (cpu_isset(rq->cpu, cpu_online_map))
-                cpu_set(rq->cpu, rd->online);
 
         for (class = sched_class_highest; class; class = class->next) {
                 if (class->join_domain)