From de82a01befdd33f6a1c050c7f888e2fa9949f48e Mon Sep 17 00:00:00 2001 From: "Srivatsa S. Bhat" Date: Tue, 11 Mar 2014 02:06:37 +0530 Subject: [PATCH] x86, msr: 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 msr code in x86 by using this latter form of callback registration. Cc: "H. Peter Anvin" Cc: Thomas Gleixner Cc: Ingo Molnar Signed-off-by: Srivatsa S. Bhat Signed-off-by: Rafael J. Wysocki --- arch/x86/kernel/msr.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c index 05266b5aae22..c9603ac80de5 100644 --- a/arch/x86/kernel/msr.c +++ b/arch/x86/kernel/msr.c @@ -259,14 +259,15 @@ static int __init msr_init(void) goto out_chrdev; } msr_class->devnode = msr_devnode; - get_online_cpus(); + + cpu_notifier_register_begin(); for_each_online_cpu(i) { err = msr_device_create(i); if (err != 0) goto out_class; } - register_hotcpu_notifier(&msr_class_cpu_notifier); - put_online_cpus(); + __register_hotcpu_notifier(&msr_class_cpu_notifier); + cpu_notifier_register_done(); err = 0; goto out; @@ -275,7 +276,7 @@ out_class: i = 0; for_each_online_cpu(i) msr_device_destroy(i); - put_online_cpus(); + cpu_notifier_register_done(); class_destroy(msr_class); out_chrdev: __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr"); @@ -286,13 +287,14 @@ out: static void __exit msr_exit(void) { int cpu = 0; - get_online_cpus(); + + cpu_notifier_register_begin(); for_each_online_cpu(cpu) msr_device_destroy(cpu); class_destroy(msr_class); __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr"); - unregister_hotcpu_notifier(&msr_class_cpu_notifier); - put_online_cpus(); + __unregister_hotcpu_notifier(&msr_class_cpu_notifier); + cpu_notifier_register_done(); } module_init(msr_init);