From 1f9b657cae637ec657aa92a5d7616581ada70672 Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Tue, 14 Jan 2025 18:07:38 -0500 Subject: [PATCH] migration: Adjust locking in migration_maybe_pause() In migration_maybe_pause() QEMU may yield BQL before waiting for a semaphore. However it yields the BQL too early, which logically gives it chance for the main thread to quickly take the BQL and modify the state to CANCELLING. To avoid such race condition from happening at all, always update the migration states within the BQL. It'll make sure no concurrent cancellation can ever happen. With that, IIUC there's chance we can remove the extra parameter in migration_maybe_pause() to update active state, but that'll be done separately later. Signed-off-by: Peter Xu Tested-by: Jiri Denemark Reviewed-by: Juraj Marcin Link: https://lore.kernel.org/r/20250114230746.3268797-9-peterx@redhat.com Signed-off-by: Fabiano Rosas --- migration/migration.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/migration/migration.c b/migration/migration.c index 03e3631d5b..4e4bf8ffed 100644 --- a/migration/migration.c +++ b/migration/migration.c @@ -2828,14 +2828,14 @@ static int migration_maybe_pause(MigrationState *s, * wait for the 'pause_sem' semaphore. */ if (s->state != MIGRATION_STATUS_CANCELLING) { - bql_unlock(); migrate_set_state(&s->state, *current_active_state, MIGRATION_STATUS_PRE_SWITCHOVER); + bql_unlock(); qemu_sem_wait(&s->pause_sem); + bql_lock(); migrate_set_state(&s->state, MIGRATION_STATUS_PRE_SWITCHOVER, new_state); *current_active_state = new_state; - bql_lock(); } return s->state == new_state ? 0 : -EINVAL; -- 2.39.5