passthrough: release assigned PCI devices earlier during domain shutdown

At least with xend, where there's not even a tool stack side attempt to
de-assign devices during domain shutdown, this allows immediate re-
starts of a domain to work reliably. (There's no apparent reason why
c/s 18010:c1577f094ae4 chose to put this in the asynchronous part of
domain destruction).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/ia64/xen/domain.c
+++ b/xen/arch/ia64/xen/domain.c
@@ -673,10 +673,8 @@ void arch_domain_destroy(struct domain *
 		free_xenheap_pages(d->shared_info,
 				   get_order_from_shift(XSI_SHIFT));
 
-	if ( iommu_enabled && need_iommu(d) )	{
-		pci_release_devices(d);
+	if ( iommu_enabled && need_iommu(d) )
 		iommu_domain_destroy(d);
-	}
 
 	tlb_track_destroy(d);
 
@@ -1721,6 +1719,8 @@ int domain_relinquish_resources(struct d
 
 	switch (d->arch.relres) {
 	case RELRES_not_started:
+		pci_release_devices(d);
+
 		/* Relinquish guest resources for VT-i domain. */
 		if (is_hvm_domain(d))
 			vmx_relinquish_guest_resources(d);
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -657,7 +657,6 @@ void arch_domain_destroy(struct domain *
         xfree(d->arch.pv_domain.e820);
 
     vmce_destroy_msr(d);
-    pci_release_devices(d);
     free_domain_pirqs(d);
     if ( !is_idle_domain(d) )
         iommu_domain_destroy(d);
@@ -2101,6 +2100,8 @@ int domain_relinquish_resources(struct d
     switch ( d->arch.relmem )
     {
     case RELMEM_not_started:
+        pci_release_devices(d);
+
         /* Tear down paging-assistance stuff. */
         paging_teardown(d);
 
--- a/xen/drivers/passthrough/iommu.c
+++ b/xen/drivers/passthrough/iommu.c
@@ -574,7 +574,8 @@ int iommu_do_domctl(
         break;
 
     case XEN_DOMCTL_assign_device:
-        if ( unlikely((d = get_domain_by_id(domctl->domain)) == NULL) )
+        if ( unlikely((d = get_domain_by_id(domctl->domain)) == NULL) ||
+             unlikely(d->is_dying) )
         {
             printk(XENLOG_G_ERR
                    "XEN_DOMCTL_assign_device: get_domain_by_id() failed\n");