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 <linux/delay.h> > 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: NChristian Borntraeger <borntraeger@de.ibm.com> Signed-off-by: NAvi Kivity <avi@redhat.com>
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