[PATCH] migration: Attempt disk reactivation in more failure scenarios

[Eric Blake <eblake@redhat.com>]

Commit fe904ea824 added a fail_inactivate label, which tries to
reactivate disks on the source after a failure while s->state ==
MIGRATION_STATUS_ACTIVE, but didn't actually use the label if
qemu_savevm_state_complete_precopy() failed.  This failure to
reactivate is also present in commit 6039dd5b1c (also covering the new
s->state == MIGRATION_STATUS_DEVICE state) and 403d18ae (ensuring
s->block_inactive is set more reliably).

Consolidate the two labels back into one - no matter HOW migration is
failed, if there is any chance we can reach vm_start() after having
attempted inactivation, it is essential that we have tried to restart
disks before then.  This also makes the cleanup more like
migrate_fd_cancel().

Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
---
 migration/migration.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/migration/migration.c b/migration/migration.c
index abcadbb619e..7f982bd2c80 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -2299,6 +2299,11 @@ static void migration_completion(MigrationState *s)
                                             MIGRATION_STATUS_DEVICE);
             }
             if (ret >= 0) {
+                /*
+                 * Inactivate disks except in COLO, and track that we
+                 * have done so in order to remember to reactivate
+                 * them if migration fails or is cancelled.
+                 */
                 s->block_inactive = !migrate_colo();
                 qemu_file_set_rate_limit(s->to_dst_file, INT64_MAX);
                 ret = qemu_savevm_state_complete_precopy(s->to_dst_file, false,
@@ -2343,13 +2348,13 @@ static void migration_completion(MigrationState *s)
         rp_error = await_return_path_close_on_source(s);
         trace_migration_return_path_end_after(rp_error);
         if (rp_error) {
-            goto fail_invalidate;
+            goto fail;
         }
     }

     if (qemu_file_get_error(s->to_dst_file)) {
         trace_migration_completion_file_err();
-        goto fail_invalidate;
+        goto fail;
     }

     if (migrate_colo() && s->state == MIGRATION_STATUS_ACTIVE) {
@@ -2363,26 +2368,25 @@ static void migration_completion(MigrationState *s)

     return;

-fail_invalidate:
-    /* If not doing postcopy, vm_start() will be called: let's regain
-     * control on images.
-     */
-    if (s->state == MIGRATION_STATUS_ACTIVE ||
-        s->state == MIGRATION_STATUS_DEVICE) {
+fail:
+    if (s->block_inactive && (s->state == MIGRATION_STATUS_ACTIVE ||
+                              s->state == MIGRATION_STATUS_DEVICE)) {
+        /*
+         * If not doing postcopy, vm_start() will be called: let's
+         * regain control on images.
+         */
         Error *local_err = NULL;

         qemu_mutex_lock_iothread();
         bdrv_activate_all(&local_err);
         if (local_err) {
             error_report_err(local_err);
-            s->block_inactive = true;
         } else {
             s->block_inactive = false;
         }
         qemu_mutex_unlock_iothread();
     }

-fail:
     migrate_set_state(&s->state, current_active_state,
                       MIGRATION_STATUS_FAILED);
 }

base-commit: b5f47ba73b7c1457d2f18d71c00e1a91a76fe60b
-- 
2.40.1