[PATCH] qemu-kvm: fix error handling in msix vector add

["Michael S. Tsirkin" <mst@redhat.com>]

When adding a vector fails, the used counter should
not be incremented, otherwise on vector change we will
try to update the routing entry.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/msix.c |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/hw/msix.c b/hw/msix.c
index 5f77dc9..47cbdc7 100644
--- a/hw/msix.c
+++ b/hw/msix.c
@@ -502,13 +502,19 @@ void msix_reset(PCIDevice *dev)
 /* Mark vector as used. */
 int msix_vector_use(PCIDevice *dev, unsigned vector)
 {
+    int ret;
     if (vector >= dev->msix_entries_nr)
         return -EINVAL;
-    if (dev->msix_entry_used[vector]++)
+    if (dev->msix_entry_used[vector]) {
         return 0;
+    }
     if (kvm_enabled() && qemu_kvm_irqchip_in_kernel()) {
-        return kvm_msix_add(dev, vector);
+        ret = kvm_msix_add(dev, vector);
+        if (ret) {
+            return ret;
+        }
     }
+    ++dev->msix_entry_used[vector];
     return 0;
 }
 
-- 
1.6.2.5