[PATCH v2 41/52] oprofile, nmi-timer: Fix CPU hotplug callback registration

From: Srivatsa S. Bhat
Date: Fri Feb 14 2014 - 03:04:12 EST


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 nmi-timer code in oprofile by using this latter form of callback
registration.

Cc: Robert Richter <rric@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
---

drivers/oprofile/nmi_timer_int.c | 23 +++++++++++++----------
1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/drivers/oprofile/nmi_timer_int.c b/drivers/oprofile/nmi_timer_int.c
index 76f1c93..9559829 100644
--- a/drivers/oprofile/nmi_timer_int.c
+++ b/drivers/oprofile/nmi_timer_int.c
@@ -108,8 +108,8 @@ static void nmi_timer_shutdown(void)
struct perf_event *event;
int cpu;

- get_online_cpus();
- unregister_cpu_notifier(&nmi_timer_cpu_nb);
+ cpu_notifier_register_begin();
+ __unregister_cpu_notifier(&nmi_timer_cpu_nb);
for_each_possible_cpu(cpu) {
event = per_cpu(nmi_timer_events, cpu);
if (!event)
@@ -119,7 +119,7 @@ static void nmi_timer_shutdown(void)
perf_event_release_kernel(event);
}

- put_online_cpus();
+ cpu_notifier_register_done();
}

static int nmi_timer_setup(void)
@@ -132,20 +132,23 @@ static int nmi_timer_setup(void)
do_div(period, HZ);
nmi_timer_attr.sample_period = period;

- get_online_cpus();
- err = register_cpu_notifier(&nmi_timer_cpu_nb);
+ cpu_notifier_register_begin();
+ err = __register_cpu_notifier(&nmi_timer_cpu_nb);
if (err)
goto out;
+
/* can't attach events to offline cpus: */
for_each_online_cpu(cpu) {
err = nmi_timer_start_cpu(cpu);
- if (err)
- break;
+ if (err) {
+ cpu_notifier_register_done();
+ nmi_timer_shutdown();
+ return err;
+ }
}
- if (err)
- nmi_timer_shutdown();
+
out:
- put_online_cpus();
+ cpu_notifier_register_done();
return err;
}


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