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 thermal throttle code in x86 by using this latter form of callback
registration.
Cc: Tony Luck <tony.l...@intel.com>
Cc: Borislav Petkov <b...@alien8.de>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Ingo Molnar <mi...@kernel.org>
Cc: "H. Peter Anvin" <h...@zytor.com>
Cc: x...@kernel.org
Cc: linux-e...@vger.kernel.org
Signed-off-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
---
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..e05dfa3 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_notifier_register_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_notifier_register_done();
+
return 0;
}
device_initcall(thermal_throttle_init_device);
--
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