[PATCH 4/4] migration: Make sure that we don't call write() in case of error

[Juan Quintela]

If we are exiting due to an error/finish/.... Just don't try to even
touch the channel with one IO operation.

Signed-off-by: Juan Quintela <quint...@redhat.com>
---
 migration/ram.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/migration/ram.c b/migration/ram.c
index 4b44578e57..909ef6d237 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1601,6 +1601,12 @@ struct {
     QemuSemaphore channels_ready;
     /* multifd ops */
     MultiFDMethods *ops;
+    /*
+     * Have we already run terminate threads.  There is a race when it
+     * happens that we got one error while we are exiting.
+     * We will use atomic operations.  Only valid values are 0 and 1.
+     */
+    int exiting;
 } *multifd_send_state;
 
 /*
@@ -1629,6 +1635,10 @@ static int multifd_send_pages(RAMState *rs)
     MultiFDPages_t *pages = multifd_send_state->pages;
     uint64_t transferred;
 
+    if (atomic_read(&multifd_send_state->exiting)) {
+        return -1;
+    }
+
     qemu_sem_wait(&multifd_send_state->channels_ready);
     for (i = next_channel;; i = (i + 1) % migrate_multifd_channels()) {
         p = &multifd_send_state->params[i];
@@ -1710,6 +1720,10 @@ static void multifd_send_terminate_threads(Error *err)
         }
     }
 
+    if (atomic_xchg(&multifd_send_state->exiting, 1)) {
+        return;
+    }
+
     for (i = 0; i < migrate_multifd_channels(); i++) {
         MultiFDSendParams *p = &multifd_send_state->params[i];
 
@@ -1824,6 +1838,10 @@ static void *multifd_send_thread(void *opaque)
 
     while (true) {
         qemu_sem_wait(&p->sem);
+
+        if (atomic_read(&multifd_send_state->exiting)) {
+            break;
+        }
         qemu_mutex_lock(&p->mutex);
 
         if (p->pending_job) {
@@ -1938,6 +1956,7 @@ int multifd_save_setup(Error **errp)
     multifd_send_state->pages = multifd_pages_init(page_count);
     qemu_sem_init(&multifd_send_state->channels_ready, 0);
     multifd_send_state->ops = multifd_ops[migrate_multifd_method()];
+    atomic_set(&multifd_send_state->exiting, 0);
 
     for (i = 0; i < thread_count; i++) {
         MultiFDSendParams *p = &multifd_send_state->params[i];
-- 
2.23.0