From 70d9e1e5940c9680f574124fe8cc02e4ce97f790 Mon Sep 17 00:00:00 2001
From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Date: Wed, 13 Apr 2022 12:33:29 +0100
Subject: [PATCH] migration: Read state once

RH-Author: Dr. David Alan Gilbert <dgilbert@redhat.com>
RH-MergeRequest: 252: migration: Read state once
RH-Bugzilla: 2168217
RH-Acked-by: Stefano Garzarella <sgarzare@redhat.com>
RH-Acked-by: Peter Xu <peterx@redhat.com>
RH-Acked-by: quintela1 <quintela@redhat.com>
RH-Commit: [1/1] 3f707ccf62e5ac2973f7e8816c50cc48e0bd646c

The 'status' field for the migration is updated normally using
an atomic operation from the migration thread.
Most readers of it aren't that careful, and in most cases it doesn't
matter.

In query_migrate->fill_source_migration_info the 'state'
is read twice; the first time to decide which state fields to fill in,
and then secondly to copy the state to the status field; that can end up
with a status that's inconsistent; e.g. setting up the fields
for 'setup' and then having an 'active' status.  In that case
libvirt gets upset by the lack of ram info.
The symptom is:
   libvirt.libvirtError: internal error: migration was active, but no RAM info was set

Read the state exactly once in fill_source_migration_info.

This is a possible fix for:
https://bugzilla.redhat.com/show_bug.cgi?id=2074205

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20220413113329.103696-1-dgilbert@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
(cherry picked from commit 552de79bfdd5e9e53847eb3c6d6e4cd898a4370e)
---
 migration/migration.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/migration/migration.c b/migration/migration.c
index 51e6726dac..d8b24a2c91 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1071,6 +1071,7 @@ static void populate_disk_info(MigrationInfo *info)
 static void fill_source_migration_info(MigrationInfo *info)
 {
     MigrationState *s = migrate_get_current();
+    int state = qatomic_read(&s->state);
     GSList *cur_blocker = migration_blockers;
 
     info->blocked_reasons = NULL;
@@ -1090,7 +1091,7 @@ static void fill_source_migration_info(MigrationInfo *info)
     }
     info->has_blocked_reasons = info->blocked_reasons != NULL;
 
-    switch (s->state) {
+    switch (state) {
     case MIGRATION_STATUS_NONE:
         /* no migration has happened ever */
         /* do not overwrite destination migration status */
@@ -1135,7 +1136,7 @@ static void fill_source_migration_info(MigrationInfo *info)
         info->has_status = true;
         break;
     }
-    info->status = s->state;
+    info->status = state;
 }
 
 typedef enum WriteTrackingSupport {
-- 
2.37.3