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 mce 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/mce.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 4d5419b..9b7734b 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -2434,14 +2434,18 @@ static __init int mcheck_init_device(void)
if (err)
return err;
+ cpu_notifier_register_begin();
for_each_online_cpu(i) {
err = mce_device_create(i);
- if (err)
+ if (err) {
+ cpu_notifier_register_done();
return err;
+ }
}
register_syscore_ops(&mce_syscore_ops);
- register_hotcpu_notifier(&mce_cpu_notifier);
+ __register_hotcpu_notifier(&mce_cpu_notifier);
+ cpu_notifier_register_done();
/* register character device /dev/mcelog */
misc_register(&mce_chrdev_device);
--
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