From 6b09b4d33bd964f49d07d3cabfb4204d58cf9811 Mon Sep 17 00:00:00 2001
From: Jeffle Xu <jefflexu@linux.alibaba.com>
Date: Mon, 22 Feb 2021 14:54:52 +0800
Subject: [PATCH] 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 <jefflexu@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
block/blk-sysfs.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index ae39c7f3d83d..0f4f0c8a7825 100644
--- 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;
}