[PATCH 19/51] x86,therm_throt.c: Fix CPU hotplug callback registration

From: Srivatsa S. Bhat
Date: Wed Feb 05 2014 - 17:13:34 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_maps_update_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_maps_update_done();


Fix the thermal throttle code in x86 by using this latter form of callback
registration.

Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-edac@xxxxxxxxxxxxxxx
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
---

arch/x86/kernel/cpu/mcheck/therm_throt.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/mcheck/therm_throt.c b/arch/x86/kernel/cpu/mcheck/therm_throt.c
index 3eec7de..c0de00a 100644
--- a/arch/x86/kernel/cpu/mcheck/therm_throt.c
+++ b/arch/x86/kernel/cpu/mcheck/therm_throt.c
@@ -319,7 +319,7 @@ static __init int thermal_throttle_init_device(void)
if (!atomic_read(&therm_throt_en))
return 0;

- register_hotcpu_notifier(&thermal_throttle_cpu_notifier);
+ cpu_maps_update_begin();

#ifdef CONFIG_HOTPLUG_CPU
mutex_lock(&therm_cpu_lock);
@@ -333,6 +333,9 @@ static __init int thermal_throttle_init_device(void)
mutex_unlock(&therm_cpu_lock);
#endif

+ __register_hotcpu_notifier(&thermal_throttle_cpu_notifier);
+ cpu_maps_update_done();
+
return 0;
}
device_initcall(thermal_throttle_init_device);

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