multifd_send_state->channels_ready is initialized to 0. It is proper to
let main thread know we are ready when thread start running.

Current implementation works since ram_save_setup() calls
multifd_send_sync_main() which wake up send thread and posts
channels_ready. This behavior will introduce some unpredictable
situation and disturb the semaphore value.

This is a preparation patch to use another mechanism to do send thread
synchronization to avoid post channels_ready in this case. So this patch
posts channels_ready when send threads start running.

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
---
 migration/ram.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/migration/ram.c b/migration/ram.c
index a4e7587648..f9e53ac413 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1093,6 +1093,8 @@ static void *multifd_send_thread(void *opaque)
     }
     /* initial packet */
     p->num_packets = 1;
+    /* let main thread know we are ready */
+    qemu_sem_post(&multifd_send_state->channels_ready);
 
     while (true) {
         qemu_sem_wait(&p->sem);
-- 
2.19.1