Messages in this thread Patch in this message |  | | From | "Srivatsa S. Bhat" <> | Subject | [PATCH v2 39/52] clocksource, dummy-timer: Fix CPU hotplug callback registration | Date | Fri, 14 Feb 2014 13:28:05 +0530 |
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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 <daniel.lezcano@linaro.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@kernel.org> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> ---
drivers/clocksource/dummy_timer.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/drivers/clocksource/dummy_timer.c b/drivers/clocksource/dummy_timer.c index b3eb582..ad35725 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);
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