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

block: don't allow the same type rq_qos add more than once

In our test of iocost, we encountered some list add/del corruptions of
inner_walk list in ioc_timer_fn.

The reason can be described as follows:

cpu 0					cpu 1
ioc_qos_write				ioc_qos_write

ioc = q_to_ioc(queue);
if (!ioc) {
        ioc = kzalloc();
					ioc = q_to_ioc(queue);
					if (!ioc) {
						ioc = kzalloc();
						...
						rq_qos_add(q, rqos);
					}
        ...
        rq_qos_add(q, rqos);
        ...
}

When the io.cost.qos file is written by two cpus concurrently, rq_qos may
be added to one disk twice. In that case, there will be two iocs enabled
and running on one disk. They own different iocgs on their active list. In
the ioc_timer_fn function, because of the iocgs from two iocs have the
same root iocg, the root iocg's walk_list may be overwritten by each other
and this leads to list add/del corruptions in building or destroying the
inner_walk list.

And so far, the blk-rq-qos framework works in case that one instance for
one type rq_qos per queue by default. This patch make this explicit and
also fix the crash above.

https://git.kernel.org/stable/c/08ef66e800a85afc6b54cb95841f6502627eee2e

https://git.kernel.org/stable/c/0b7f5d7a4d2a72ad9de04ab8ccba2a31904aa638

https://git.kernel.org/stable/c/0c9bb1acd1d103a3070b2126870eb52761d606ce

https://git.kernel.org/stable/c/14a6e2eb7df5c7897c15b109cba29ab0c4a791b6