migration: Improve migration thread error handling

We now report errors also when we finish migration, not only on info
migrate.  We plan to use this error from several places, and we want
the first error to happen to win, so we add an mutex to order it.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

3 files changed, 22 insertions, 5 deletions

diff --git a/migration/migration.c b/migration/migration.c
index a058f8b..62761d5 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1084,19 +1084,30 @@ static void migrate_fd_cleanup(void *opaque)
                           MIGRATION_STATUS_CANCELLED);
     }
 
+    if (s->error) {
+        /* It is used on info migrate.  We can't free it */
+        error_report_err(error_copy(s->error));
+    }
     notifier_list_notify(&migration_state_notifiers, s);
     block_cleanup_parameters(s);
 }
 
+void migrate_set_error(MigrationState *s, const Error *error)
+{
+    qemu_mutex_lock(&s->error_mutex);
+    if (!s->error) {
+        s->error = error_copy(error);
+    }
+    qemu_mutex_unlock(&s->error_mutex);
+}
+
 void migrate_fd_error(MigrationState *s, const Error *error)
 {
     trace_migrate_fd_error(error_get_pretty(error));
     assert(s->to_dst_file == NULL);
     migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
                       MIGRATION_STATUS_FAILED);
-    if (!s->error) {
-        s->error = error_copy(error);
-    }
+    migrate_set_error(s, error);
     notifier_list_notify(&migration_state_notifiers, s);
     block_cleanup_parameters(s);
 }
@@ -2427,6 +2438,7 @@ static void migration_instance_finalize(Object *obj)
     MigrationState *ms = MIGRATION_OBJ(obj);
     MigrationParameters *params = &ms->parameters;
 
+    qemu_mutex_destroy(&ms->error_mutex);
     g_free(params->tls_hostname);
     g_free(params->tls_creds);
     qemu_sem_destroy(&ms->pause_sem);
@@ -2441,6 +2453,7 @@ static void migration_instance_init(Object *obj)
     ms->xbzrle_cache_size = DEFAULT_MIGRATE_CACHE_SIZE;
     ms->mbps = -1;
     qemu_sem_init(&ms->pause_sem, 0);
+    qemu_mutex_init(&ms->error_mutex);
 
     params->tls_hostname = g_strdup("");
     params->tls_creds = g_strdup("");
diff --git a/migration/migration.h b/migration/migration.h
index cd988a9..8ccdd7a 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -132,8 +132,12 @@ struct MigrationState
     int64_t colo_checkpoint_time;
     QEMUTimer *colo_delay_timer;
 
-    /* The last error that occurred */
+    /* The first error that has occurred.
+       We used the mutex to be able to return the 1st error message */
     Error *error;
+    /* mutex to protect errp */
+    QemuMutex error_mutex;
+
     /* Do we have to clean up -b/-i from old migrate parameters */
     /* This feature is deprecated and will be removed */
     bool must_remove_block_options;
@@ -162,6 +166,7 @@ bool  migration_has_all_channels(void);
 
 uint64_t migrate_max_downtime(void);
 
+void migrate_set_error(MigrationState *s, const Error *error);
 void migrate_fd_error(MigrationState *s, const Error *error);
 
 void migrate_fd_connect(MigrationState *s);
diff --git a/migration/tls.c b/migration/tls.c
index 596e879..026a008 100644
--- a/migration/tls.c
+++ b/migration/tls.c
@@ -119,7 +119,6 @@ static void migration_tls_outgoing_handshake(QIOTask *task,
     if (qio_task_propagate_error(task, &err)) {
         trace_migration_tls_outgoing_handshake_error(error_get_pretty(err));
         migrate_fd_error(s, err);
-        error_free(err);
     } else {
         trace_migration_tls_outgoing_handshake_complete();
         migration_channel_connect(s, ioc, NULL);