migration: Maybe VM is paused when migration is cancelled

If the migration is cancelled when it is in the completion phase,
the migration state is set to MIGRATION_STATUS_CANCELLING.
The VM maybe wait for the 'pause_sem' semaphore in migration_maybe_pause
function, so that VM always is paused.

Reported-by: Euler Robot <euler.robot@huawei.com>
Signed-off-by: Zhimin Feng <fengzhimin1@huawei.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

migration/migration.c

@@ -2797,14 +2797,22 @@ static int migration_maybe_pause(MigrationState *s,
         /* This block intentionally left blank */
     }
 
-    qemu_mutex_unlock_iothread();
-    migrate_set_state(&s->state, *current_active_state,
-                      MIGRATION_STATUS_PRE_SWITCHOVER);
-    qemu_sem_wait(&s->pause_sem);
-    migrate_set_state(&s->state, MIGRATION_STATUS_PRE_SWITCHOVER,
-                      new_state);
-    *current_active_state = new_state;
-    qemu_mutex_lock_iothread();
+    /*
+     * If the migration is cancelled when it is in the completion phase,
+     * the migration state is set to MIGRATION_STATUS_CANCELLING.
+     * So we don't need to wait a semaphore, otherwise we would always
+     * wait for the 'pause_sem' semaphore.
+     */
+    if (s->state != MIGRATION_STATUS_CANCELLING) {
+        qemu_mutex_unlock_iothread();
+        migrate_set_state(&s->state, *current_active_state,
+                          MIGRATION_STATUS_PRE_SWITCHOVER);
+        qemu_sem_wait(&s->pause_sem);
+        migrate_set_state(&s->state, MIGRATION_STATUS_PRE_SWITCHOVER,
+                          new_state);
+        *current_active_state = new_state;
+        qemu_mutex_lock_iothread();
+    }
 
     return s->state == new_state ? 0 : -EINVAL;
 }