From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoffer Dall Subject: Re: [PATCH 2/3] KVM: arm64: vgic-its: Plug race in vgic_put_irq Date: Tue, 9 Aug 2016 12:20:19 +0200 Message-ID: <20160809102019.GC9175@cbox> References: <20160803161325.14933-1-christoffer.dall@linaro.org> <20160803161325.14933-3-christoffer.dall@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Marc Zyngier , kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org To: Andre Przywara Return-path: Received: from mail-wm0-f52.google.com ([74.125.82.52]:37850 "EHLO mail-wm0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751337AbcHIKSb (ORCPT ); Tue, 9 Aug 2016 06:18:31 -0400 Received: by mail-wm0-f52.google.com with SMTP id i5so24387233wmg.0 for ; Tue, 09 Aug 2016 03:18:31 -0700 (PDT) Content-Disposition: inline In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On Mon, Aug 08, 2016 at 12:20:14PM +0100, Andre Przywara wrote: > Hi, > > On 03/08/16 17:13, Christoffer Dall wrote: > > Right now the following sequence of events can happen: > > > > 1. Thread X calls vgic_put_irq > > 2. Thread Y calls vgic_add_lpi > > 3. Thread Y gets lpi_list_lock > > 4. Thread X drops the ref count to 0 and blocks on lpi_list_lock > > 5. Thread Y finds the irq via the lpi_list_lock, raises the ref > > count to 1, and release the lpi_list_lock. > > 6. Thread X proceeds and frees the irq. > > > > Avoid this by holding the spinlock around the kref_put. > > > > Signed-off-by: Christoffer Dall > > --- > > virt/kvm/arm/vgic/vgic.c | 20 ++++++++++---------- > > 1 file changed, 10 insertions(+), 10 deletions(-) > > > > diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c > > index e7aeac7..fb8c0ab 100644 > > --- a/virt/kvm/arm/vgic/vgic.c > > +++ b/virt/kvm/arm/vgic/vgic.c > > @@ -117,22 +117,22 @@ static void vgic_irq_release(struct kref *ref) > > > > void vgic_put_irq(struct kvm *kvm, struct vgic_irq *irq) > > { > > - struct vgic_dist *dist; > > + struct vgic_dist *dist = &kvm->arch.vgic; > > > > if (irq->intid < VGIC_MIN_LPI) > > return; > > > > - if (!kref_put(&irq->refcount, vgic_irq_release)) > > - return; > > - > > - dist = &kvm->arch.vgic; > > - > > spin_lock(&dist->lpi_list_lock); > > - list_del(&irq->lpi_list); > > - dist->lpi_list_count--; > > - spin_unlock(&dist->lpi_list_lock); > > + if (!kref_put(&irq->refcount, vgic_irq_release)) { > > + spin_unlock(&dist->lpi_list_lock); > > + return; > > + } else { > > Just a nit, I guess, but we don't need this "else" since the if-branch > always returns? > correct, I can change that. > > + list_del(&irq->lpi_list); > > + dist->lpi_list_count--; > > + spin_unlock(&dist->lpi_list_lock); > > > > - kfree(irq); > > + kfree(irq); > > + } > > } > > > > /** > > > > Otherwise: > > Reviewed-by: Andre Przywara > Thanks. -Christoffer