[PATCH] check return value of cpu_callback

Spawing ksoftirqd, migration, or watchdog, and calling init_timers_cpu()
may fail with small memory.  If it happens in initcalls, kernel NULL
pointer dereference happens later.  This patch makes crash happen
immediately in such cases.  It seems a bit better than getting kernel NULL
pointer dereference later.

Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: NAkinobu Mita <mita@miraclelinux.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

kernel/sched.c

@@ -5272,9 +5272,11 @@ static struct notifier_block __cpuinitdata migration_notifier = {
 int __init migration_init(void)
 {
 	void *cpu = (void *)(long)smp_processor_id();
+	int err;
 
 	/* Start one for the boot CPU: */
-	migration_call(&migration_notifier, CPU_UP_PREPARE, cpu);
+	err = migration_call(&migration_notifier, CPU_UP_PREPARE, cpu);
+	BUG_ON(err == NOTIFY_BAD);
 	migration_call(&migration_notifier, CPU_ONLINE, cpu);
 	register_cpu_notifier(&migration_notifier);
 

kernel/softirq.c

@@ -612,7 +612,9 @@ static struct notifier_block __cpuinitdata cpu_nfb = {
 __init int spawn_ksoftirqd(void)
 {
 	void *cpu = (void *)(long)smp_processor_id();
-	cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
+	int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
+
+	BUG_ON(err == NOTIFY_BAD);
 	cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
 	register_cpu_notifier(&cpu_nfb);
 	return 0;

kernel/softlockup.c

@@ -149,8 +149,9 @@ static struct notifier_block __cpuinitdata cpu_nfb = {
 __init void spawn_softlockup_task(void)
 {
 	void *cpu = (void *)(long)smp_processor_id();
+	int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
 
-	cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
+	BUG_ON(err == NOTIFY_BAD);
 	cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
 	register_cpu_notifier(&cpu_nfb);
 

kernel/timer.c

@@ -1694,8 +1694,10 @@ static struct notifier_block __cpuinitdata timers_nb = {
 
 void __init init_timers(void)
 {
-	timer_cpu_notify(&timers_nb, (unsigned long)CPU_UP_PREPARE,
+	int err = timer_cpu_notify(&timers_nb, (unsigned long)CPU_UP_PREPARE,
 				(void *)(long)smp_processor_id());
+
+	BUG_ON(err == NOTIFY_BAD);
 	register_cpu_notifier(&timers_nb);
 	open_softirq(TIMER_SOFTIRQ, run_timer_softirq, NULL);
 }