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Date: Tue,  2 Apr 2024 08:49:23 +0200
From: Greg Kroah-Hartman <>
Cc: Greg Kroah-Hartman <>
Subject: CVE-2024-26671: blk-mq: fix IO hang from sbitmap wakeup race


In the Linux kernel, the following vulnerability has been resolved:

blk-mq: fix IO hang from sbitmap wakeup race

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 \

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.

The Linux kernel CVE team has assigned CVE-2024-26671 to this issue.

Affected and fixed versions

	Fixed in 4.19.307 with commit 9525b38180e2
	Fixed in 5.4.269 with commit ecd7744a1446
	Fixed in 5.10.210 with commit 7610ba131925
	Fixed in 5.15.149 with commit 89e0e66682e1
	Fixed in 6.1.77 with commit 1d9c777d3e70
	Fixed in 6.6.16 with commit 6d8b01624a25
	Fixed in 6.7.4 with commit f1bc0d8163f8
	Fixed in 6.8 with commit 5266caaf5660

Please see for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files

The file(s) affected by this issue are:


The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:

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