[PATCH] cpu hotplug: fix CPU_UP_CANCEL handling

If a cpu hotplug callback fails on CPU_UP_PREPARE, all callbacks will be
called with CPU_UP_CANCELED.  A few of these callbacks assume that on
CPU_UP_PREPARE a pointer to task has been stored in a percpu array.  This
assumption is not true if CPU_UP_PREPARE fails and the following calls to
kthread_bind() in CPU_UP_CANCELED will cause an addressing exception
because of passing a NULL pointer.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index f8d540b324ca..f06d059edef5 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4756,6 +4756,8 @@ static int migration_call(struct notifier_block *nfb, unsigned long action,
                 break;
 #ifdef CONFIG_HOTPLUG_CPU
         case CPU_UP_CANCELED:
+                if (!cpu_rq(cpu)->migration_thread)
+                        break;
                 /* Unbind it from offline cpu so it can run.  Fall thru. */
                 kthread_bind(cpu_rq(cpu)->migration_thread,
                              any_online_cpu(cpu_online_map));