From: Heiko Carstens 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 Cc: Ashok Raj Signed-off-by: Andrew Morton --- kernel/sched.c | 2 ++ kernel/softirq.c | 2 ++ kernel/softlockup.c | 2 ++ kernel/workqueue.c | 2 ++ 4 files changed, 8 insertions(+) diff -puN kernel/sched.c~cpu-hotplug-fix-cpu_up_cancel-handling kernel/sched.c --- a/kernel/sched.c~cpu-hotplug-fix-cpu_up_cancel-handling +++ a/kernel/sched.c @@ -4754,6 +4754,8 @@ static int migration_call(struct notifie 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)); diff -puN kernel/softirq.c~cpu-hotplug-fix-cpu_up_cancel-handling kernel/softirq.c --- a/kernel/softirq.c~cpu-hotplug-fix-cpu_up_cancel-handling +++ a/kernel/softirq.c @@ -470,6 +470,8 @@ static int cpu_callback(struct notifier_ break; #ifdef CONFIG_HOTPLUG_CPU case CPU_UP_CANCELED: + if (!per_cpu(ksoftirqd, hotcpu)) + break; /* Unbind so it can run. Fall thru. */ kthread_bind(per_cpu(ksoftirqd, hotcpu), any_online_cpu(cpu_online_map)); diff -puN kernel/softlockup.c~cpu-hotplug-fix-cpu_up_cancel-handling kernel/softlockup.c --- a/kernel/softlockup.c~cpu-hotplug-fix-cpu_up_cancel-handling +++ a/kernel/softlockup.c @@ -127,6 +127,8 @@ cpu_callback(struct notifier_block *nfb, break; #ifdef CONFIG_HOTPLUG_CPU case CPU_UP_CANCELED: + if (!per_cpu(watchdog_task, hotcpu)) + break; /* Unbind so it can run. Fall thru. */ kthread_bind(per_cpu(watchdog_task, hotcpu), any_online_cpu(cpu_online_map)); diff -puN kernel/workqueue.c~cpu-hotplug-fix-cpu_up_cancel-handling kernel/workqueue.c --- a/kernel/workqueue.c~cpu-hotplug-fix-cpu_up_cancel-handling +++ a/kernel/workqueue.c @@ -590,6 +590,8 @@ static int workqueue_cpu_callback(struct case CPU_UP_CANCELED: list_for_each_entry(wq, &workqueues, list) { + if (!per_cpu_ptr(wq->cpu_wq, hotcpu)->thread) + continue; /* Unbind so it can run. */ kthread_bind(per_cpu_ptr(wq->cpu_wq, hotcpu)->thread, any_online_cpu(cpu_online_map)); _