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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>
This commit is contained in:
Jeffle Xu 2021-02-22 14:54:52 +08:00 committed by Jens Axboe
parent b357e4a694
commit 6b09b4d33b
1 changed files with 5 additions and 2 deletions
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7
block/blk-sysfs.c
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@ -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;
}