[RHEL6.0 PATCH] qemu-kvm: fix crash on reboot with vhost-net

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

Bugzilla: 585940
Upstream status: applied on qemu-kvm.git,
commit 992cc816c433332f2e93db033919a9ddbfcd1da4

When vhost-net is disabled on reboot, we set msix mask notifier
to NULL to disable further mask/unmask notifications.
Code currently tries to pass this NULL to notifier,
leading to a crash.  The right thing to do is
to add explicit APIs to enable/disable notifications.
Now when disabling notifications:
- if vector is masked, we don't need to notify backend,
  just disable future notifications
- if vector is unmasked, invoke callback to unassign backend,
  then disable future notifications

This patch also polls notifier before closing it,
to make sure we don't lose events if poll callback
didn't have time to run.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/msix.c       |   40 +++++++++++++++++++++++++++++++++++-----
 hw/msix.h       |    1 +
 hw/virtio-pci.c |    7 +++++--
 3 files changed, 41 insertions(+), 7 deletions(-)

diff --git a/hw/msix.c b/hw/msix.c
index 3fcf3a1..94e3981 100644
--- a/hw/msix.c
+++ b/hw/msix.c
@@ -610,14 +610,44 @@ void msix_unuse_all_vectors(PCIDevice *dev)
 
 int msix_set_mask_notifier(PCIDevice *dev, unsigned vector, void *opaque)
 {
+    int r;
+    if (vector >= dev->msix_entries_nr || !dev->msix_entry_used[vector])
+        return 0;
+
+    assert(dev->msix_mask_notifier);
+    assert(opaque);
+    assert(!dev->msix_mask_notifier_opaque[vector]);
+
+    if (msix_is_masked(dev, vector)) {
+        return 0;
+    }
+    r = dev->msix_mask_notifier(dev, vector, opaque,
+                                msix_is_masked(dev, vector));
+    if (r < 0) {
+        return r;
+    }
+    dev->msix_mask_notifier_opaque[vector] = opaque;
+    return r;
+}
+
+int msix_unset_mask_notifier(PCIDevice *dev, unsigned vector)
+{
     int r = 0;
     if (vector >= dev->msix_entries_nr || !dev->msix_entry_used[vector])
         return 0;
 
-    if (dev->msix_mask_notifier)
-        r = dev->msix_mask_notifier(dev, vector, opaque,
-                                    msix_is_masked(dev, vector));
-    if (r >= 0)
-        dev->msix_mask_notifier_opaque[vector] = opaque;
+    assert(dev->msix_mask_notifier);
+    assert(dev->msix_mask_notifier_opaque[vector]);
+
+    if (msix_is_masked(dev, vector)) {
+        return 0;
+    }
+    r = dev->msix_mask_notifier(dev, vector,
+                                dev->msix_mask_notifier_opaque[vector],
+                                msix_is_masked(dev, vector));
+    if (r < 0) {
+        return r;
+    }
+    dev->msix_mask_notifier_opaque[vector] = NULL;
     return r;
 }
diff --git a/hw/msix.h b/hw/msix.h
index f167231..6b21ffb 100644
--- a/hw/msix.h
+++ b/hw/msix.h
@@ -34,4 +34,5 @@ void msix_reset(PCIDevice *dev);
 extern int msix_supported;
 
 int msix_set_mask_notifier(PCIDevice *dev, unsigned vector, void *opaque);
+int msix_unset_mask_notifier(PCIDevice *dev, unsigned vector);
 #endif
diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
index cba188c..22f7fa0 100644
--- a/hw/virtio-pci.c
+++ b/hw/virtio-pci.c
@@ -437,10 +437,13 @@ static int virtio_pci_guest_notifier(void *opaque, int n, bool assign)
         msix_set_mask_notifier(&proxy->pci_dev,
                                virtio_queue_vector(proxy->vdev, n), vq);
     } else {
-        msix_set_mask_notifier(&proxy->pci_dev,
-                               virtio_queue_vector(proxy->vdev, n), NULL);
+        msix_unset_mask_notifier(&proxy->pci_dev,
+				 virtio_queue_vector(proxy->vdev, n));
         qemu_set_fd_handler(event_notifier_get_fd(notifier),
                             NULL, NULL, NULL);
+        /* Test and clear notifier before closing it,
+         * in case poll callback didn't have time to run. */
+        virtio_pci_guest_notifier_read(vq);
         event_notifier_cleanup(notifier);
     }
 
-- 
1.7.1.rc1.22.g3163