icount: fix deadlock when all cpus are sleeping

When all cpus are sleeping (e.g in WFI), to avoid a deadlock
in the main_loop, wake it up in order to start the warp timer.
Signed-off-by: NClement Deschamps <clement.deschamps@greensocs.com>
Message-Id: <20181021142103.19014-1-clement.deschamps@greensocs.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

cpus.c

@@ -1554,6 +1554,14 @@ static void *qemu_tcg_rr_cpu_thread_fn(void *arg)
             atomic_mb_set(&cpu->exit_request, 0);
         }
 
+        if (use_icount && all_cpu_threads_idle()) {
+            /*
+             * When all cpus are sleeping (e.g in WFI), to avoid a deadlock
+             * in the main_loop, wake it up in order to start the warp timer.
+             */
+            qemu_notify_event();
+        }
+
         qemu_tcg_rr_wait_io_event(cpu ? cpu : first_cpu);
         deal_with_unplugged_cpus();
     }