Commit 0169005b authored by Ming Lei's avatar Ming Lei Committed by Li Lingfeng
Browse files

blk-mq: fix IO hang from sbitmap wakeup race 

mainline inclusion
from mainline-v6.8-rc1
commit 5266caaf5660529e3da53004b8b7174cab6374ed
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I943Q7
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5266caaf5660529e3da53004b8b7174cab6374ed



--------------------------------

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: default avatarChanghui Zhong <czhong@redhat.com>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20240112122626.4181044-1-ming.lei@redhat.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
Signed-off-by: default avatarLi Lingfeng <lilingfeng3@huawei.com>
parent a5194e63

block/blk-mq.c

+16 −0
Original line number Diff line number Diff line
@@ -1277,6 +1277,22 @@ 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