block: fix potential IO hang when turning off io_poll

QUEUE_FLAG_POLL flag will be cleared when turning off 'io_poll', while at that moment there may be IOs stuck in hw queue uncompleted. The following polling routine won't help reap these IOs, since blk_poll() will return immediately because of cleared QUEUE_FLAG_POLL flag. Thus these IOs will hang until they finnaly time out. The hang out can be observed by 'fio --engine=io_uring iodepth=1', while turning off 'io_poll' at the same time. To fix this, freeze and flush the request queue first when turning off 'io_poll'. Signed-off-by: Jeffle Xu <[email protected]> Signed-off-by: Jens Axboe <[email protected]>
fracktal · Feb 22, 2021 · 6b09b4d · 6b09b4d
1 parent b357e4a
commit 6b09b4d
Showing 1 changed file with 5 additions and 2 deletions.
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
@@ -434,10 +434,13 @@ static ssize_t queue_poll_store(struct request_queue *q, const char *page,
 	if (ret < 0)
 		return ret;
 
-	if (poll_on)
+	if (poll_on) {
 		blk_queue_flag_set(QUEUE_FLAG_POLL, q);
-	else
+	} else {
+		blk_mq_freeze_queue(q);
 		blk_queue_flag_clear(QUEUE_FLAG_POLL, q);
+		blk_mq_unfreeze_queue(q);
+	}
 
 	return ret;
 }