cpu hotplug: adjust root-domain->online span in response to hotplug event
Gregory Haskins [Sat, 8 Mar 2008 05:10:15 +0000 (00:10 -0500)]
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>

kernel/sched.c

index 52b9867..b02e4fc 100644 (file)
@@ -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)