octeon, watchdog: 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 watchdog code in octeon by using this latter form of callback
registration.

Cc: Wim Van Sebroeck <wim@iguana.be>
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>

1 files changed, 9 insertions, 2 deletions

diff --git a/drivers/watchdog/octeon-wdt-main.c b/drivers/watchdog/octeon-wdt-main.c
index 461208831428..4baf2d788920 100644
--- a/drivers/watchdog/octeon-wdt-main.c
+++ b/drivers/watchdog/octeon-wdt-main.c
@@ -708,10 +708,13 @@ static int __init octeon_wdt_init(void)
 
 	cpumask_clear(&irq_enabled_cpus);
 
+	cpu_notifier_register_begin();
 	for_each_online_cpu(cpu)
 		octeon_wdt_setup_interrupt(cpu);
 
-	register_hotcpu_notifier(&octeon_wdt_cpu_notifier);
+	__register_hotcpu_notifier(&octeon_wdt_cpu_notifier);
+	cpu_notifier_register_done();
+
 out:
 	return ret;
 }
@@ -725,7 +728,8 @@ static void __exit octeon_wdt_cleanup(void)
 
 	misc_deregister(&octeon_wdt_miscdev);
 
-	unregister_hotcpu_notifier(&octeon_wdt_cpu_notifier);
+	cpu_notifier_register_begin();
+	__unregister_hotcpu_notifier(&octeon_wdt_cpu_notifier);
 
 	for_each_online_cpu(cpu) {
 		int core = cpu2core(cpu);
@@ -734,6 +738,9 @@ static void __exit octeon_wdt_cleanup(void)
 		/* Free the interrupt handler */
 		free_irq(OCTEON_IRQ_WDOG0 + core, octeon_wdt_poke_irq);
 	}
+
+	cpu_notifier_register_done();
+
 	/*
 	 * Disable the boot-bus memory, the code it points to is soon
 	 * to go missing.