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blk-mq: fix IO hang from sbitmap wakeup race

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In blk_mq_mark_tag_wait(), __add_wait_queue() may be re-ordered
with the following blk_mq_get_driver_tag() in case of getting driver
tag failure.

Then in __sbitmap_queue_wake_up(), waitqueue_active() may not observe
the added waiter in blk_mq_mark_tag_wait() and wake up nothing, meantime
blk_mq_mark_tag_wait() can't get driver tag successfully.

This issue can be reproduced by running the following test in loop, and
fio hang can be observed in < 30min when running it on my test VM
in laptop.

	modprobe -r scsi_debug
	modprobe scsi_debug delay=0 dev_size_mb=4096 max_queue=1 host_max_queue=1 submit_queues=4
	dev=`ls -d /sys/bus/pseudo/drivers/scsi_debug/adapter*/host*/target*/*/block/* | head -1 | xargs basename`
	fio --filename=/dev/"$dev" --direct=1 --rw=randrw --bs=4k --iodepth=1 \
       		--runtime=100 --numjobs=40 --time_based --name=test \
        	--ioengine=libaio

Fix the issue by adding one explicit barrier in blk_mq_mark_tag_wait(), which
is just fine in case of running out of tag.

Cc: Jan Kara <jack@suse.cz>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Reported-by: Changhui Zhong <czhong@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20240112122626.4181044-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2024-01-12 20:26:26 +08:00 committed by Jens Axboe
parent b2da197565
commit 5266caaf56
1 changed files with 16 additions and 0 deletions
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16
block/blk-mq.c
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@ -1852,6 +1852,22 @@ static bool blk_mq_mark_tag_wait(struct blk_mq_hw_ctx *hctx,
wait->flags &= ~WQ_FLAG_EXCLUSIVE;
__add_wait_queue(wq, wait);
/*
* Add one explicit barrier since blk_mq_get_driver_tag() may
* not imply barrier in case of failure.
*
* Order adding us to wait queue and allocating driver tag.
*
* The pair is the one implied in sbitmap_queue_wake_up() which
* orders clearing sbitmap tag bits and waitqueue_active() in
* __sbitmap_queue_wake_up(), since waitqueue_active() is lockless
*
* Otherwise, re-order of adding wait queue and getting driver tag
* may cause __sbitmap_queue_wake_up() to wake up nothing because
* the waitqueue_active() may not observe us in wait queue.
*/
smp_mb();
/*
* It's possible that a tag was freed in the window between the
* allocation failure and adding the hardware queue to the wait