vfio/pci: call irq_bypass_unregister_producer() before freeing irq

Since irq_bypass_register_producer() is called after request_irq(), we
should do tear-down in reverse order: irq_bypass_unregister_producer()
then free_irq().

Specifically free_irq() may release resources required by the
irqbypass del_producer() callback.  Notably an example provided by
Marc Zyngier on arm64 with GICv4 that he indicates has the potential
to wedge the hardware:

 free_irq(irq)
   __free_irq(irq)
     irq_domain_deactivate_irq(irq)
       its_irq_domain_deactivate()
         [unmap the VLPI from the ITS]

 kvm_arch_irq_bypass_del_producer(cons, prod)
   kvm_vgic_v4_unset_forwarding(kvm, irq, ...)
     its_unmap_vlpi(irq)
       [Unmap the VLPI from the ITS (again), remap the original LPI]

Signed-off-by: Jiang Yi <[email protected]>
Cc: [email protected] # v4.4+
Fixes: 6d7425f ("vfio: Register/unregister irq_bypass_producer")
Link: https://lore.kernel.org/kvm/[email protected]
Reviewed-by: Marc Zyngier <[email protected]>
Reviewed-by: Eric Auger <[email protected]>
[aw: commit log]
Signed-off-by: Alex Williamson <[email protected]>

Author: Jiang Yi

drivers/vfio/pci/vfio_pci_intrs.c

@@ -294,8 +294,8 @@ static int vfio_msi_set_vector_signal(struct vfio_pci_device *vdev,
 	irq = pci_irq_vector(pdev, vector);
 
 	if (vdev->ctx[vector].trigger) {
-		free_irq(irq, vdev->ctx[vector].trigger);
 		irq_bypass_unregister_producer(&vdev->ctx[vector].producer);
+		free_irq(irq, vdev->ctx[vector].trigger);
 		kfree(vdev->ctx[vector].name);
 		eventfd_ctx_put(vdev->ctx[vector].trigger);
 		vdev->ctx[vector].trigger = NULL;