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oprofile, nmi-timer: Fix CPU hotplug callback registration

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

Cc: Robert Richter <rric@kernel.org>
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>
This commit is contained in:
Srivatsa S. Bhat 2014-03-11 02:10:36 +05:30 committed by Rafael J. Wysocki
parent 07494d547e
commit 180d864632
1 changed files with 13 additions and 10 deletions
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23
drivers/oprofile/nmi_timer_int.c
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@ -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;
}