[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/workqueue.c b/kernel/workqueue.c
index f869aff6bc0c..565cf7a1febd 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -590,6 +590,8 @@ static int workqueue_cpu_callback(struct notifier_block *nfb,
 
         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));