[PATCH v2 39/52] 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(_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(_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
---
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(_timer_cpu_nb);
+ int err = 0;
+
+ cpu_notifier_register_begin();
+ err = __register_cpu_notifier(_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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[PATCH v2 39/52] 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 daniel.lezc...@linaro.org
Cc: Thomas Gleixner t...@linutronix.de
Cc: Ingo Molnar mi...@kernel.org
Signed-off-by: Srivatsa S. Bhat srivatsa.b...@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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