[PATCH] cpu hoptlug: avoid usage of smp_processor_id() in preemptible code

Replace smp_processor_id() with any_online_cpu(cpu_online_map) in order to
avoid lots of "BUG: using smp_processor_id() in preemptible [00000001]
code:..." messages in case taking a cpu online fails.

All the traces start at the last notifier_call_chain(...) in kernel/cpu.c.
Since we hold the cpu_control semaphore it shouldn't be any problem to access
cpu_online_map.

The reason why cpu_up failed is simply that the cpu that was supposed to be
taken online wasn't even there.  That is because on s390 we never know when a
new cpu comes and therefore cpu_possible_map consists of only ones and doesn't
reflect reality.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index b4f4eb613537..013f1448006b 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4680,7 +4680,8 @@ static int migration_call(struct notifier_block *nfb, unsigned long action,
 #ifdef CONFIG_HOTPLUG_CPU
         case CPU_UP_CANCELED:
                 /* Unbind it from offline cpu so it can run.  Fall thru. */
-                kthread_bind(cpu_rq(cpu)->migration_thread,smp_processor_id());
+                kthread_bind(cpu_rq(cpu)->migration_thread,
+                             any_online_cpu(cpu_online_map));
                 kthread_stop(cpu_rq(cpu)->migration_thread);
                 cpu_rq(cpu)->migration_thread = NULL;
                 break;