[PATCH] PCI: avoid bogus calls to get_pseg()

[Jan Beulich <jbeulich@xxxxxxxx>]

When passed -1, the function (taking a u16) will look for segment
0xffff, which might exist. If it exists, we may find (return) the wrong
device.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
An alternative would be to declare that both functions cannot be called
with "wildcards" anymore. The last such use went away with f591755823a7
("IOMMU/PCI: don't let domain cleanup continue when device de-assignment
failed") afaict.

Each time I look at this pair of functions I wonder why we have two
copies of almost the same code (with a curious difference of only one
having ASSERT(pcidevs_locked())). Any opinions on deleting either one,
subsuming its functionality into the other one by allowing the domain
pointer to be NULL to signify "any"?

--- a/xen/drivers/passthrough/pci.c
+++ b/xen/drivers/passthrough/pci.c
@@ -578,20 +578,19 @@ int __init pci_ro_device(int seg, int bu
 
 struct pci_dev *pci_get_pdev(int seg, int bus, int devfn)
 {
-    struct pci_seg *pseg = get_pseg(seg);
+    struct pci_seg *pseg = NULL;
     struct pci_dev *pdev = NULL;
 
     ASSERT(pcidevs_locked());
     ASSERT(seg != -1 || bus == -1);
     ASSERT(bus != -1 || devfn == -1);
 
+    if ( seg == -1 )
+        radix_tree_gang_lookup(&pci_segments, (void **)&pseg, 0, 1);
+    else
+        pseg = get_pseg(seg);
     if ( !pseg )
-    {
-        if ( seg == -1 )
-            radix_tree_gang_lookup(&pci_segments, (void **)&pseg, 0, 1);
-        if ( !pseg )
-            return NULL;
-    }
+        return NULL;
 
     do {
         list_for_each_entry ( pdev, &pseg->alldevs_list, alldevs_list )
@@ -628,19 +627,18 @@ struct pci_dev *pci_get_real_pdev(int se
 struct pci_dev *pci_get_pdev_by_domain(const struct domain *d, int seg,
                                        int bus, int devfn)
 {
-    struct pci_seg *pseg = get_pseg(seg);
+    struct pci_seg *pseg = NULL;
     struct pci_dev *pdev = NULL;
 
     ASSERT(seg != -1 || bus == -1);
     ASSERT(bus != -1 || devfn == -1);
 
+    if ( seg == -1 )
+        radix_tree_gang_lookup(&pci_segments, (void **)&pseg, 0, 1);
+    else
+        pseg = get_pseg(seg);
     if ( !pseg )
-    {
-        if ( seg == -1 )
-            radix_tree_gang_lookup(&pci_segments, (void **)&pseg, 0, 1);
-        if ( !pseg )
-            return NULL;
-    }
+        return NULL;
 
     do {
         list_for_each_entry ( pdev, &pseg->alldevs_list, alldevs_list )