[Qemu-devel] [PATCH 2/3] migration: fix migrate_cancel leads live_migration thread hung forever

[Ivan Ren]

When we 'migrate_cancel' a multifd migration, live_migration thread may
hung forever at some points, because of multifd_send_thread has already
exit for socket error:
1. multifd_send_pages may hung at qemu_sem_wait(&multifd_send_state->
   channels_ready)
2. multifd_send_sync_main my hung at qemu_sem_wait(&multifd_send_state->
   sem_sync)

Signed-off-by: Ivan Ren <address@hidden>
---
 migration/ram.c | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/migration/ram.c b/migration/ram.c
index f8908286c2..e4eb9c441f 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1097,7 +1097,11 @@ static void *multifd_send_thread(void *opaque)
 {
     MultiFDSendParams *p = opaque;
     Error *local_err = NULL;
-    int ret;
+    int ret = 0;
+
+    uint32_t used = 0;
+    uint64_t packet_num = 0;
+    uint32_t flags = 0;
 
     trace_multifd_send_thread_start(p->id);
     rcu_register_thread();
@@ -1113,9 +1117,9 @@ static void *multifd_send_thread(void *opaque)
         qemu_mutex_lock(&p->mutex);
 
         if (p->pending_job) {
-            uint32_t used = p->pages->used;
-            uint64_t packet_num = p->packet_num;
-            uint32_t flags = p->flags;
+            used = p->pages->used;
+            packet_num = p->packet_num;
+            flags = p->flags;
 
             p->next_packet_size = used * qemu_target_page_size();
             multifd_send_fill_packet(p);
@@ -1164,6 +1168,17 @@ out:
         multifd_send_terminate_threads(local_err);
     }
 
+    /*
+     * Error happen, I will exit, but I can't just leave, tell
+     * who pay attention to me.
+     */
+    if (ret != 0) {
+        if (flags & MULTIFD_FLAG_SYNC) {
+            qemu_sem_post(&multifd_send_state->sem_sync);
+        }
+        qemu_sem_post(&multifd_send_state->channels_ready);
+    }
+
     qemu_mutex_lock(&p->mutex);
     p->running = false;
     qemu_mutex_unlock(&p->mutex);
-- 
2.17.2 (Apple Git-113)