KVM: Fix possible circular locking in kvm_vm_ioctl_assign_device()
One possible order is:
KVM_CREATE_IRQCHIP ioctl(took kvm->lock) -> kvm_iobus_register_dev() ->
down_write(kvm->slots_lock).
The other one is in kvm_vm_ioctl_assign_device(), which take kvm->slots_lock
first, then kvm->lock.
Update the comment of lock order as well.
Observe it due to kernel locking debug warnings.
Cc: stable@kernel.org
Signed-off-by: Sheng Yang <sheng@linux.intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
index fd9c097..f73de63 100644
--- a/virt/kvm/assigned-dev.c
+++ b/virt/kvm/assigned-dev.c
@@ -508,8 +508,8 @@
struct kvm_assigned_dev_kernel *match;
struct pci_dev *dev;
- down_read(&kvm->slots_lock);
mutex_lock(&kvm->lock);
+ down_read(&kvm->slots_lock);
match = kvm_find_assigned_dev(&kvm->arch.assigned_dev_head,
assigned_dev->assigned_dev_id);
@@ -573,8 +573,8 @@
}
out:
- mutex_unlock(&kvm->lock);
up_read(&kvm->slots_lock);
+ mutex_unlock(&kvm->lock);
return r;
out_list_del:
list_del(&match->list);
@@ -585,8 +585,8 @@
pci_dev_put(dev);
out_free:
kfree(match);
- mutex_unlock(&kvm->lock);
up_read(&kvm->slots_lock);
+ mutex_unlock(&kvm->lock);
return r;
}