ia64, err-inject: Fix CPU hotplug callback registration

Subsystems that want to register CPU hotplug callbacks, as well as perform
initialization for the CPUs that are already online, often do it as shown
below:

	get_online_cpus();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	register_cpu_notifier(&foobar_cpu_notifier);

	put_online_cpus();

This is wrong, since it is prone to ABBA deadlocks involving the
cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
with CPU hotplug operations).

Instead, the correct and race-free way of performing the callback
registration is:

	cpu_notifier_register_begin();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	/* Note the use of the double underscored version of the API */
	__register_cpu_notifier(&foobar_cpu_notifier);

	cpu_notifier_register_done();

Fix the error injection code in ia64 by using this latter form of callback
registration.

Cc: Tony Luck <tony.luck@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/arch/ia64/kernel/err_inject.c b/arch/ia64/kernel/err_inject.c
index f59c0b844e8855ea55989ad6b814fad125b45879..0c161ed6d18e6d77433c8bafabfdd48f904a077d 100644 (file)
--- a/arch/ia64/kernel/err_inject.c
+++ b/arch/ia64/kernel/err_inject.c
@@ -269,12 +269,17 @@ err_inject_init(void)
 #ifdef ERR_INJ_DEBUG
        printk(KERN_INFO "Enter error injection driver.\n");
 #endif
+
+       cpu_notifier_register_begin();
+
        for_each_online_cpu(i) {
                err_inject_cpu_callback(&err_inject_cpu_notifier, CPU_ONLINE,
                                (void *)(long)i);
        }
 
-       register_hotcpu_notifier(&err_inject_cpu_notifier);
+       __register_hotcpu_notifier(&err_inject_cpu_notifier);
+
+       cpu_notifier_register_done();
 
        return 0;
 }
@@ -288,11 +293,17 @@ err_inject_exit(void)
 #ifdef ERR_INJ_DEBUG
        printk(KERN_INFO "Exit error injection driver.\n");
 #endif
+
+       cpu_notifier_register_begin();
+
        for_each_online_cpu(i) {
                sys_dev = get_cpu_device(i);
                sysfs_remove_group(&sys_dev->kobj, &err_inject_attr_group);
        }
-       unregister_hotcpu_notifier(&err_inject_cpu_notifier);
+
+       __unregister_hotcpu_notifier(&err_inject_cpu_notifier);
+
+       cpu_notifier_register_done();
 }
 
 module_init(err_inject_init);