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/intc/arm_gicv3_its_kvm.c b/hw/intc/arm_gicv3_its_kvm.c
index ad0ebab..46835ed 100644
--- a/hw/intc/arm_gicv3_its_kvm.c
+++ b/hw/intc/arm_gicv3_its_kvm.c
@@ -91,7 +91,6 @@ static void vm_change_state_handler(void *opaque, int running,
 static void kvm_arm_its_realize(DeviceState *dev, Error **errp)
 {
     GICv3ITSState *s = ARM_GICV3_ITS_COMMON(dev);
-    Error *local_err = NULL;
 
     s->dev_fd = kvm_create_device(kvm_state, KVM_DEV_TYPE_ARM_VGIC_ITS, false);
     if (s->dev_fd < 0) {
@@ -113,9 +112,7 @@ static void kvm_arm_its_realize(DeviceState *dev, Error **errp)
         GITS_CTLR)) {
         error_setg(&s->migration_blocker, "This operating system kernel "
                    "does not support vITS migration");
-        migrate_add_blocker(s->migration_blocker, &local_err);
-        if (local_err) {
-            error_propagate(errp, local_err);
+        if (migrate_add_blocker(s->migration_blocker, errp) < 0) {
             error_free(s->migration_blocker);
             return;
         }