From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Yang, Sheng" Subject: Re: [PATCH 1/1] KVM: Fix potentially recursively get kvm lock Date: Wed, 13 May 2009 10:07:54 +0800 Message-ID: <200905131007.55189.sheng.yang@intel.com> References: <200905121705.53176.sheng.yang@intel.com> <1242164187.4788.4.camel@2710p.home> <20090512220908.GA22626@amt.cnet> Mime-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-15" Content-Transfer-Encoding: 7bit Cc: Alex Williamson , Avi Kivity , "kvm@vger.kernel.org" To: Marcelo Tosatti Return-path: Received: from mga11.intel.com ([192.55.52.93]:57523 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751371AbZEMCHH (ORCPT ); Tue, 12 May 2009 22:07:07 -0400 In-Reply-To: <20090512220908.GA22626@amt.cnet> Content-Disposition: inline Sender: kvm-owner@vger.kernel.org List-ID: On Wednesday 13 May 2009 06:09:08 Marcelo Tosatti wrote: > On Tue, May 12, 2009 at 03:36:27PM -0600, Alex Williamson wrote: > > On Tue, 2009-05-12 at 16:44 -0300, Marcelo Tosatti wrote: > > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > > > index 4d00942..ba067db 100644 > > > --- a/virt/kvm/kvm_main.c > > > +++ b/virt/kvm/kvm_main.c > > > @@ -250,7 +250,15 @@ static void deassign_host_irq(struct kvm *kvm, > > > disable_irq_nosync(assigned_dev-> > > > host_msix_entries[i].vector); > > > > > > + /* > > > + * FIXME: kvm_assigned_dev_interrupt_work_handler can deadlock > > > + * with cancel_work_sync, since it requires kvm->lock for irq > > > + * injection. This is a hack, the irq code must use > > > + * a separate lock. > > > + */ > > > + mutex_unlock(&kvm->lock); > > > cancel_work_sync(&assigned_dev->interrupt_work); > > > + mutex_lock(&kvm->lock); > > > > Seems to work, I assume you've got a similar unlock/lock for the > > MSI/INTx block. Thanks, > > KVM: workaround workqueue / deassign_host_irq deadlock > > I think I'm running into the following deadlock in the kvm kernel module > when trying to use device assignment: > > CPU A CPU B > kvm_vm_ioctl_deassign_dev_irq() > mutex_lock(&kvm->lock); worker_thread() > -> kvm_deassign_irq() -> > kvm_assigned_dev_interrupt_work_handler() > -> deassign_host_irq() mutex_lock(&kvm->lock); > -> cancel_work_sync() [blocked] > > Workaround the issue by dropping kvm->lock for cancel_work_sync(). > > Reported-by: Alex Williamson > From: Sheng Yang > Signed-off-by: Marcelo Tosatti Another calling path(kvm_free_all_assigned_devices()) don't hold kvm->lock... Seems it need the lock for travel assigned dev list? -- regards Yang, Sheng > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 4d00942..d4af719 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -250,7 +250,15 @@ static void deassign_host_irq(struct kvm *kvm, > disable_irq_nosync(assigned_dev-> > host_msix_entries[i].vector); > > + /* > + * FIXME: kvm_assigned_dev_interrupt_work_handler can deadlock > + * with cancel_work_sync, since it requires kvm->lock for irq > + * injection. This is a hack, the irq code must use > + * a separate lock. Same below for MSI. > + */ > + mutex_unlock(&kvm->lock); > cancel_work_sync(&assigned_dev->interrupt_work); > + mutex_lock(&kvm->lock); > > for (i = 0; i < assigned_dev->entries_nr; i++) > free_irq(assigned_dev->host_msix_entries[i].vector, > @@ -263,7 +271,9 @@ static void deassign_host_irq(struct kvm *kvm, > } else { > /* Deal with MSI and INTx */ > disable_irq_nosync(assigned_dev->host_irq); > + mutex_unlock(&kvm->lock); > cancel_work_sync(&assigned_dev->interrupt_work); > + mutex_lock(&kvm->lock); > > free_irq(assigned_dev->host_irq, (void *)assigned_dev);