linux-kernel - [PATCH v2 37/52] acpi-cpufreq: Fix CPU hotplug callback registration

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Message-ID: <20140214075736.22701.78024.stgit@srivatsabhat.in.ibm.com>
Date:	Fri, 14 Feb 2014 13:27:37 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	paulus@...ba.org, oleg@...hat.com, mingo@...nel.org,
	rusty@...tcorp.com.au, peterz@...radead.org, tglx@...utronix.de,
	akpm@...ux-foundation.org
Cc:	paulmck@...ux.vnet.ibm.com, tj@...nel.org, walken@...gle.com,
	ego@...ux.vnet.ibm.com, linux@....linux.org.uk, rjw@...ysocki.net,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	srivatsa.bhat@...ux.vnet.ibm.com,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Ingo Molnar <mingo@...nel.org>, cpufreq@...r.kernel.org,
	linux-pm@...r.kernel.org, Viresh Kumar <viresh.kumar@...aro.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Subject: [PATCH v2 37/52] acpi-cpufreq: 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 acpi-cpufreq code by using this latter form of callback registration.

Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: cpufreq@...r.kernel.org
Cc: linux-pm@...r.kernel.org
Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
---

 drivers/cpufreq/acpi-cpufreq.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
index 18448a7..245ae078e 100644
--- a/drivers/cpufreq/acpi-cpufreq.c
+++ b/drivers/cpufreq/acpi-cpufreq.c
@@ -907,15 +907,16 @@ static void __init acpi_cpufreq_boost_init(void)
 
 		acpi_cpufreq_driver.boost_supported = true;
 		acpi_cpufreq_driver.boost_enabled = boost_state(0);
-		get_online_cpus();
+
+		cpu_notifier_register_begin();
 
 		/* Force all MSRs to the same value */
 		boost_set_msrs(acpi_cpufreq_driver.boost_enabled,
 			       cpu_online_mask);
 
-		register_cpu_notifier(&boost_nb);
+		__register_cpu_notifier(&boost_nb);
 
-		put_online_cpus();
+		cpu_notifier_register_done();
 	}
 }
 

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