From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>

multifd_send() function is currently not thread safe, make it thread safe
by holding a lock during its execution.

This way it will be possible to safely call it concurrently from multiple
threads.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
---
 migration/multifd.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/migration/multifd.c b/migration/multifd.c
index 9578a985449b..4575495c8816 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -50,6 +50,10 @@ typedef struct {
 
 struct {
     MultiFDSendParams *params;
+
+    /* multifd_send() body is not thread safe, needs serialization */
+    QemuMutex multifd_send_mutex;
+
     /*
      * Global number of generated multifd packets.
      *
@@ -331,6 +335,7 @@ static void multifd_send_kick_main(MultiFDSendParams *p)
  */
 bool multifd_send(MultiFDSendData **send_data)
 {
+    QEMU_LOCK_GUARD(&multifd_send_state->multifd_send_mutex);
     int i;
     static int next_channel;
     MultiFDSendParams *p = NULL; /* make happy gcc */
@@ -508,6 +513,7 @@ static void multifd_send_cleanup_state(void)
     socket_cleanup_outgoing_migration();
     qemu_sem_destroy(&multifd_send_state->channels_created);
     qemu_sem_destroy(&multifd_send_state->channels_ready);
+    qemu_mutex_destroy(&multifd_send_state->multifd_send_mutex);
     g_free(multifd_send_state->params);
     multifd_send_state->params = NULL;
     g_free(multifd_send_state);
@@ -853,6 +859,7 @@ bool multifd_send_setup(void)
     thread_count = migrate_multifd_channels();
     multifd_send_state = g_malloc0(sizeof(*multifd_send_state));
     multifd_send_state->params = g_new0(MultiFDSendParams, thread_count);
+    qemu_mutex_init(&multifd_send_state->multifd_send_mutex);
     qemu_sem_init(&multifd_send_state->channels_created, 0);
     qemu_sem_init(&multifd_send_state->channels_ready, 0);
     qatomic_set(&multifd_send_state->exiting, 0);