From 3d3aab1b973b01bd2a1aa46307e94a1380b1d802 Mon Sep 17 00:00:00 2001 From: Christian Borntraeger Date: Tue, 2 Dec 2008 11:17:32 +0100 Subject: KVM: set owner of cpu and vm file operations 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 Signed-off-by: Avi Kivity --- virt/kvm/kvm_main.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index fd9cc79092cb..484c903544f4 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1498,7 +1498,7 @@ static int kvm_vcpu_release(struct inode *inode, struct file *filp) 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, @@ -1892,7 +1892,7 @@ static int kvm_vm_mmap(struct file *file, struct vm_area_struct *vma) 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, @@ -2256,6 +2256,8 @@ int kvm_init(void *opaque, unsigned int vcpu_size, } kvm_chardev_ops.owner = module; + kvm_vm_fops.owner = module; + kvm_vcpu_fops.owner = module; r = misc_register(&kvm_dev); if (r) { -- cgit v1.2.1