Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753043AbYLBKRs (ORCPT ); Tue, 2 Dec 2008 05:17:48 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754322AbYLBKRg (ORCPT ); Tue, 2 Dec 2008 05:17:36 -0500 Received: from mtagate6.de.ibm.com ([195.212.29.155]:55685 "EHLO mtagate6.de.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753991AbYLBKRf (ORCPT ); Tue, 2 Dec 2008 05:17:35 -0500 From: Christian Borntraeger To: Avi Kivity Subject: [PATCH 2/2] kvm: set owner of cpu and vm file operations Date: Tue, 2 Dec 2008 11:17:32 +0100 User-Agent: KMail/1.9.9 Cc: kvm@vger.kernel.org, LKML References: <200812021114.59050.borntraeger@de.ibm.com> In-Reply-To: <200812021114.59050.borntraeger@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200812021117.32521.borntraeger@de.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2718 Lines: 79 There is a race between a "close of the file descriptors" and module unload in the kvm module. You can easily trigger this problem by applying this debug patch: >--- kvm.orig/virt/kvm/kvm_main.c >+++ kvm/virt/kvm/kvm_main.c >@@ -648,10 +648,14 @@ void kvm_free_physmem(struct kvm *kvm) > kvm_free_physmem_slot(&kvm->memslots[i], NULL); > } > >+#include > static void kvm_destroy_vm(struct kvm *kvm) > { > struct mm_struct *mm = kvm->mm; > >+ printk("off1\n"); >+ msleep(5000); >+ printk("off2\n"); > spin_lock(&kvm_lock); > list_del(&kvm->vm_list); > spin_unlock(&kvm_lock); and killing the userspace, followed by an rmmod. The problem is that kvm_destroy_vm can run while the module count is 0. That means, you can remove the module while kvm_destroy_vm is running. But kvm_destroy_vm is part of the module text. This causes a kerneloops. The race exists without the msleep but is much harder to trigger. This patch requires the fix for anon_inodes (anon_inodes: use fops->owner for module refcount). With this patch, we can set the owner of all anonymous KVM inodes file operations. The VFS will then control the KVM module refcount as long as there is an open file. kvm_destroy_vm will be called by the release function of the last closed file - before the VFS drops the module refcount. Signed-off-by: Christian Borntraeger --- virt/kvm/kvm_main.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) Index: kvm/virt/kvm/kvm_main.c =================================================================== --- kvm.orig/virt/kvm/kvm_main.c +++ kvm/virt/kvm/kvm_main.c @@ -1303,7 +1303,7 @@ static int kvm_vcpu_release(struct inode return 0; } -static const struct file_operations kvm_vcpu_fops = { +static struct file_operations kvm_vcpu_fops = { .release = kvm_vcpu_release, .unlocked_ioctl = kvm_vcpu_ioctl, .compat_ioctl = kvm_vcpu_ioctl, @@ -1697,7 +1697,7 @@ static int kvm_vm_mmap(struct file *file return 0; } -static const struct file_operations kvm_vm_fops = { +static struct file_operations kvm_vm_fops = { .release = kvm_vm_release, .unlocked_ioctl = kvm_vm_ioctl, .compat_ioctl = kvm_vm_ioctl, @@ -2061,6 +2061,8 @@ int kvm_init(void *opaque, unsigned int } kvm_chardev_ops.owner = module; + kvm_vm_fops.owner = module; + kvm_vcpu_fops.owner = module; r = misc_register(&kvm_dev); if (r) { -- 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/