Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751843AbbFYMz2 (ORCPT ); Thu, 25 Jun 2015 08:55:28 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:48736 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751252AbbFYMzU (ORCPT ); Thu, 25 Jun 2015 08:55:20 -0400 Date: Thu, 25 Jun 2015 14:55:14 +0200 From: Peter Zijlstra To: Pontus Fuchs Cc: mingo@redhat.com, "linux-kernel@vger.kernel.org" , gleb@kernel.org Subject: [PATCH] sched,kvm: Fix KVM preempt_notifier usage Message-ID: <20150625125514.GA3644@twins.programming.kicks-ass.net> References: <558BED42.1030000@gmail.com> <20150625120949.GZ3644@twins.programming.kicks-ass.net> <558BF0E4.50602@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <558BF0E4.50602@gmail.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2788 Lines: 83 Subject: 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 90977418aeb6..d7aafa0458a0 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -128,8 +128,9 @@ 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; @@ -139,8 +140,8 @@ 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); } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/