error: Avoid error_propagate() after migrate_add_blocker()

When migrate_add_blocker(blocker, &errp) is followed by
error_propagate(errp, err), we can often just as well do
migrate_add_blocker(..., errp).

Do that with this Coccinelle script:

    @@
    expression blocker, err, errp;
    expression ret;
    @@
    -    ret = migrate_add_blocker(blocker, &err);
    -    if (err) {
    +    ret = migrate_add_blocker(blocker, errp);
    +    if (ret < 0) {
             ... when != err;
    -        error_propagate(errp, err);
             ...
         }

    @@
    expression blocker, err, errp;
    @@
    -    migrate_add_blocker(blocker, &err);
    -    if (err) {
    +    if (migrate_add_blocker(blocker, errp) < 0) {
             ... when != err;
    -        error_propagate(errp, err);
             ...
         }

Double-check @err is not used afterwards.  Dereferencing it would be
use after free, but checking whether it's null would be legitimate.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20200707160613.848843-43-armbru@redhat.com>

1 files changed, 1 insertions, 4 deletions

diff --git a/hw/display/virtio-gpu-base.c b/hw/display/virtio-gpu-base.c
index c159351be3..7961308606 100644
--- a/hw/display/virtio-gpu-base.c
+++ b/hw/display/virtio-gpu-base.c
@@ -128,7 +128,6 @@ virtio_gpu_base_device_realize(DeviceState *qdev,
 {
     VirtIODevice *vdev = VIRTIO_DEVICE(qdev);
     VirtIOGPUBase *g = VIRTIO_GPU_BASE(qdev);
-    Error *local_err = NULL;
     int i;
 
     if (g->conf.max_outputs > VIRTIO_GPU_MAX_SCANOUTS) {
@@ -139,9 +138,7 @@ virtio_gpu_base_device_realize(DeviceState *qdev,
     g->use_virgl_renderer = false;
     if (virtio_gpu_virgl_enabled(g->conf)) {
         error_setg(&g->migration_blocker, "virgl is not yet migratable");
-        migrate_add_blocker(g->migration_blocker, &local_err);
-        if (local_err) {
-            error_propagate(errp, local_err);
+        if (migrate_add_blocker(g->migration_blocker, errp) < 0) {
             error_free(g->migration_blocker);
             return false;
         }