From: Srivatsa S. Bhat Date: Mon, 10 Mar 2014 20:40:23 +0000 (+0530) Subject: clocksource, dummy-timer: Fix CPU hotplug callback registration X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=8daa127f4e857427c66f365f650dda90f459aa54;p=linux-beck.git clocksource, dummy-timer: 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 clocksource dummy-timer code by using this latter form of callback registration. Cc: Daniel Lezcano Cc: Thomas Gleixner Cc: Ingo Molnar Signed-off-by: Srivatsa S. Bhat Signed-off-by: Rafael J. Wysocki --- diff --git a/drivers/clocksource/dummy_timer.c b/drivers/clocksource/dummy_timer.c index b3eb582d6a6f..ad3572541728 100644 --- a/drivers/clocksource/dummy_timer.c +++ b/drivers/clocksource/dummy_timer.c @@ -56,14 +56,19 @@ static struct notifier_block dummy_timer_cpu_nb = { static int __init dummy_timer_register(void) { - int err = register_cpu_notifier(&dummy_timer_cpu_nb); + int err = 0; + + cpu_notifier_register_begin(); + err = __register_cpu_notifier(&dummy_timer_cpu_nb); if (err) - return err; + goto out; /* We won't get a call on the boot CPU, so register immediately */ if (num_possible_cpus() > 1) dummy_timer_setup(); - return 0; +out: + cpu_notifier_register_done(); + return err; } early_initcall(dummy_timer_register);