migration/block: Fix possible race with block_inactive

Src QEMU sets block_inactive=true very early before the invalidation takes
place.  It means if something wrong happened during setting the flag but
before reaching qemu_savevm_state_complete_precopy_non_iterable() where it
did the invalidation work, it'll make block_inactive flag inconsistent.

For example, think about when qemu_savevm_state_complete_precopy_iterable()
can fail: it will have block_inactive set to true even if all block drives
are active.

Fix that by only update the flag after the invalidation is done.

No Fixes for any commit, because it's not an issue if bdrv_activate_all()
is re-entrant upon all-active disks - false positive block_inactive can
bring nothing more than "trying to active the blocks but they're already
active".  However let's still do it right to avoid the inconsistent flag
v.s. reality.

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Message-Id: <20241206230838.1111496-6-peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>

diff --git a/migration/migration.c b/migration/migration.c
index c80fc7b94ccf817d30a8e6752b37ab79c9b7d2ff..fd42a549e61b750241e8ea59d001f7c0a1a85813 100644 (file)
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -2742,14 +2742,11 @@ static int migration_completion_precopy(MigrationState *s,
         goto out_unlock;
     }
 
-    /*
-     * 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();
     migration_rate_set(RATE_LIMIT_DISABLED);
+
+    /* Inactivate disks except in COLO */
     ret = qemu_savevm_state_complete_precopy(s->to_dst_file, false,
-                                             s->block_inactive);
+                                             !migrate_colo());
 out_unlock:
     bql_unlock();
     return ret;

diff --git a/migration/savevm.c b/migration/savevm.c
index d4842b519d836e9aac06c4099a8a6d0100f3adb3..3a414aff521532d8a7c12c99c8004a28b6ead306 100644 (file)
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1558,6 +1558,8 @@ int qemu_savevm_state_complete_precopy_non_iterable(QEMUFile *f,
             qemu_file_set_error(f, ret);
             return ret;
         }
+        /* Remember that we did this */
+        s->block_inactive = true;
     }
     if (!in_postcopy) {
         /* Postcopy stream will still be going */