From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933213AbdLRJIi (ORCPT ); Mon, 18 Dec 2017 04:08:38 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40532 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932858AbdLRJI2 (ORCPT ); Mon, 18 Dec 2017 04:08:28 -0500 Subject: Re: [PATCH] KVM/Eventfd: Avoid crash when assign and deassign same eventfd in parallel. To: Paolo Bonzini , Lan Tianyu Cc: rkrcmar@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, dvyukov@google.com, kernellwp@gmail.com References: <1513554007-12302-1-git-send-email-tianyu.lan@intel.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: Date: Mon, 18 Dec 2017 10:08:26 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Mon, 18 Dec 2017 09:08:28 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 18.12.2017 09:50, Paolo Bonzini wrote: > On 18/12/2017 09:30, David Hildenbrand wrote: >> The ugly thing in kvm_irqfd_assign() is that we access irqfd without >> holding a lock. I think that should rather be fixed than working around >> that issue. (e.g. lock() -> lookup again -> verify still in list -> >> unlock()) > > I wonder if it's even simpler: > > diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c > index f2ac53ab8243..17ed298bd66f 100644 > --- a/virt/kvm/eventfd.c > +++ b/virt/kvm/eventfd.c > @@ -387,7 +387,6 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args) > > idx = srcu_read_lock(&kvm->irq_srcu); > irqfd_update(kvm, irqfd); > - srcu_read_unlock(&kvm->irq_srcu, idx); > > list_add_tail(&irqfd->list, &kvm->irqfds.items); > > @@ -420,10 +419,12 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args) > irqfd->consumer.token, ret); > } > #endif > + srcu_read_unlock(&kvm->irq_srcu, idx); > Was worried about the poll() call. But if that works, it would be very nice. > return 0; > > fail: > + /* irq_srcu is *not* held here. */ > if (irqfd->resampler) > irqfd_resampler_shutdown(irqfd); > > > Thanks, > > Paolo > -- Thanks, David / dhildenb