block: don't merge across cgroup boundaries if blkcg is enabled

mainline inclusion
from mainline-v5.18-rc1
commit 6b2b0459
category: bugfix
bugzilla: 187443, https://gitee.com/openeuler/kernel/issues/I5Z7O2
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/fs?h=v6.0-rc5&id=6b2b04590b51aa4cf395fcd185ce439cab5961dc



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blk-iocost and iolatency are cgroup aware rq-qos policies but they didn't
disable merges across different cgroups. This obviously can lead to
accounting and control errors but more importantly to priority inversions -
e.g. an IO which belongs to a higher priority cgroup or IO class may end up
getting throttled incorrectly because it gets merged to an IO issued from a
low priority cgroup.

Fix it by adding blk_cgroup_mergeable() which is called from merge paths and
rejects cross-cgroup and cross-issue_as_root merges.

Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: d7067512 ("block: introduce blk-iolatency io controller")
Cc: stable@vger.kernel.org # v4.19+
Cc: Josef Bacik <jbacik@fb.com>
Link: https://lore.kernel.org/r/Yi/eE/6zFNyWJ+qd@slm.duckdns.org


Signed-off-by: Jens Axboe <axboe@kernel.dk>

conflicts:
	block/blk-merge.c
	include/linux/blk-cgroup.h

Signed-off-by: Li Nan <linan122@huawei.com>
Reviewed-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>