| From | "Srivatsa S. Bhat" <> | Subject | [PATCH 27/51] x86, kvm: Fix CPU hotplug callback registration | Date | Thu, 06 Feb 2014 03:39:35 +0530 |
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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 kvm code in x86 by using this latter form of callback registration.
Cc: Gleb Natapov <gleb@kernel.org> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: x86@kernel.org Cc: kvm@vger.kernel.org Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> ---
arch/x86/kvm/x86.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 39c28f09..e3893b7 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -5365,7 +5365,8 @@ static void kvm_timer_init(void) int cpu; max_tsc_khz = tsc_khz; - register_hotcpu_notifier(&kvmclock_cpu_notifier_block); + + cpu_maps_update_begin(); if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) { #ifdef CONFIG_CPU_FREQ struct cpufreq_policy policy; @@ -5382,6 +5383,10 @@ static void kvm_timer_init(void) pr_debug("kvm: max_tsc_khz = %ld\n", max_tsc_khz); for_each_online_cpu(cpu) smp_call_function_single(cpu, tsc_khz_changed, NULL, 1); + + __register_hotcpu_notifier(&kvmclock_cpu_notifier_block); + cpu_maps_update_done(); + } static DEFINE_PER_CPU(struct kvm_vcpu *, current_vcpu);
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