In the Linux kernel, the following vulnerability has been resolved: md: Don't ignore suspended array in md_check_recovery() mddev_suspend() never stop sync_thread, hence it doesn't make sense to ignore suspended array in md_check_recovery(), which might cause sync_thread can't be unregistered. After commit f52f5c71f3d4 ("md: fix stopping sync thread"), following hang can be triggered by test shell/integrity-caching.sh: 1) suspend the array: raid_postsuspend mddev_suspend 2) stop the array: raid_dtr md_stop __md_stop_writes stop_sync_thread set_bit(MD_RECOVERY_INTR, &mddev->recovery); md_wakeup_thread_directly(mddev->sync_thread); wait_event(..., !test_bit(MD_RECOVERY_RUNNING, &mddev->recovery)) 3) sync thread done: md_do_sync set_bit(MD_RECOVERY_DONE, &mddev->recovery); md_wakeup_thread(mddev->thread); 4) daemon thread can't unregister sync thread: md_check_recovery if (mddev->suspended) return; -> return directly md_read_sync_thread clear_bit(MD_RECOVERY_RUNNING, &mddev->recovery); -> MD_RECOVERY_RUNNING can't be cleared, hence step 2 hang; This problem is not just related to dm-raid, fix it by ignoring suspended array in md_check_recovery(). And follow up patches will improve dm-raid better to frozen sync thread during suspend.