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Date:	Thu, 24 Jul 2014 16:36:33 -0700
From:	tip-bot for Borislav Petkov <>
Subject: [tip:x86/urgent] x86, MCE: Robustify mcheck_init_device

Commit-ID:  51cbe7e7c400def749950ab6b2c120624dbe21a7
Author:     Borislav Petkov <>
AuthorDate: Fri, 20 Jun 2014 23:16:45 +0200
Committer:  Borislav Petkov <>
CommitDate: Mon, 21 Jul 2014 18:14:32 +0200

x86, MCE: Robustify mcheck_init_device

BorisO reports that misc_register() fails often on xen. The current code
unregisters the CPU hotplug notifier in that case. If then a CPU is
offlined and onlined back again, we end up with a second timer running
on that CPU, leading to soft lockups and system hangs.

So let's leave the hotcpu notifier always registered - even if
mce_device_create failed for some cores and never unreg it so that we
can deal with the timer handling accordingly.

Reported-and-Tested-by: Boris Ostrovsky <>
Signed-off-by: Borislav Petkov <>
 arch/x86/kernel/cpu/mcheck/mce.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index bb92f38..9a79c8d 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -2451,6 +2451,12 @@ static __init int mcheck_init_device(void)
 	for_each_online_cpu(i) {
 		err = mce_device_create(i);
 		if (err) {
+			/*
+			 * Register notifier anyway (and do not unreg it) so
+			 * that we don't leave undeleted timers, see notifier
+			 * callback above.
+			 */
+			__register_hotcpu_notifier(&mce_cpu_notifier);
 			goto err_device_create;
@@ -2471,10 +2477,6 @@ static __init int mcheck_init_device(void)
-	cpu_notifier_register_begin();
-	__unregister_hotcpu_notifier(&mce_cpu_notifier);
-	cpu_notifier_register_done();
 	 * We didn't keep track of which devices were created above, but
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