From: Peter Zijlstra Date: Thu, 25 Jun 2015 14:55:14 +0200 Subject: [PATCH] sched,kvm: Fix KVM preempt_notifier usage The preempt-notifier API needs to sleep with the addition of the static_key, we do however need to hold off preemption while modifying the preempt notifier list, otherwise a preemption could observe an inconsistent list state. There is no reason to have preemption disabled in the caller, registering a preempt notifier is a purely task local affair. Therefore move the preempt_disable into the functions and change the callers to a preemptible context. Cc: Gleb Natapov Fixes: 1cde2930e154 ("sched/preempt: Add static_key() to preempt_notifiers") Reported-and-Tested-by: Pontus Fuchs Signed-off-by: Peter Zijlstra (Intel) --- kernel/sched/core.c | 11 +++++++++++ virt/kvm/kvm_main.c | 5 +++-- 2 files changed, 14 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index b803e1b8ab0c..6169c167ac98 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2327,7 +2327,12 @@ static struct static_key preempt_notifier_key = STATIC_KEY_INIT_FALSE; void preempt_notifier_register(struct preempt_notifier *notifier) { static_key_slow_inc(&preempt_notifier_key); + /* + * Avoid preemption while changing the preempt notifier list. + */ + preempt_disable(); hlist_add_head(¬ifier->link, ¤t->preempt_notifiers); + preempt_enable(); } EXPORT_SYMBOL_GPL(preempt_notifier_register); @@ -2339,7 +2344,13 @@ EXPORT_SYMBOL_GPL(preempt_notifier_register); */ void preempt_notifier_unregister(struct preempt_notifier *notifier) { + /* + * Avoid preemption while changing the preempt notifier list. + */ + preempt_disable(); hlist_del(¬ifier->link); + preempt_enable(); + static_key_slow_dec(&preempt_notifier_key); } EXPORT_SYMBOL_GPL(preempt_notifier_unregister); diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 848af90b8091..7dc8d3eb9e1f 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -127,8 +127,9 @@ int vcpu_load(struct kvm_vcpu *vcpu) if (mutex_lock_killable(&vcpu->mutex)) return -EINTR; - cpu = get_cpu(); preempt_notifier_register(&vcpu->preempt_notifier); + + cpu = get_cpu(); kvm_arch_vcpu_load(vcpu, cpu); put_cpu(); return 0; @@ -138,8 +139,8 @@ void vcpu_put(struct kvm_vcpu *vcpu) { preempt_disable(); kvm_arch_vcpu_put(vcpu); - preempt_notifier_unregister(&vcpu->preempt_notifier); preempt_enable(); + preempt_notifier_unregister(&vcpu->preempt_notifier); mutex_unlock(&vcpu->mutex); }