[PULL 35/42] migration: Take BQL slightly longer in postcopy_start()

[Fabiano Rosas]

From: Peter Xu <peterx@redhat.com>

This paves way for some follow up patch to modify migration states at the
end of postcopy_start(), which should better be with the BQL so that
there's no way of concurrent cancellation.

So we'll do something slightly more with BQL but they're really trivial,
hopefully nothing will really chance with this.

A side benefit is we can drop another explicit lock() in failure path.

Signed-off-by: Peter Xu <peterx@redhat.com>
Tested-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Link: 20250114230746.3268797-11-peterx@redhat.com">https://lore.kernel.org/r/20250114230746.3268797-11-peterx@redhat.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>
---
 migration/migration.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/migration/migration.c b/migration/migration.c
index 5a3d0750ec..4ba6c8912a 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -2753,8 +2753,6 @@ static int postcopy_start(MigrationState *ms, Error 
**errp)
 
     migration_downtime_end(ms);
 
-    bql_unlock();
-
     if (migrate_postcopy_ram()) {
         /*
          * Although this ping is just for debug, it could potentially be
@@ -2770,7 +2768,6 @@ static int postcopy_start(MigrationState *ms, Error 
**errp)
     ret = qemu_file_get_error(ms->to_dst_file);
     if (ret) {
         error_setg_errno(errp, -ret, "postcopy_start: Migration stream error");
-        bql_lock();
         goto fail;
     }
     trace_postcopy_preempt_enabled(migrate_postcopy_preempt());
@@ -2781,6 +2778,8 @@ static int postcopy_start(MigrationState *ms, Error 
**errp)
      */
     migration_rate_set(migrate_max_postcopy_bandwidth());
 
+    bql_unlock();
+
     return ret;
 
 fail_closefb:
-- 
2.35.3