Revert "Revert "block, bfq: honor already-setup queue merges""

stable inclusion
from stable-v5.10.110
commit cc051f497eac9d8a0d816cd4bffa3415f2724871
bugzilla: https://gitee.com/openeuler/kernel/issues/I574AL

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cc051f497eac9d8a0d816cd4bffa3415f2724871

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

[ Upstream commit 15729ff8 ]

A crash [1] happened to be triggered in conjunction with commit
2d52c58b ("block, bfq: honor already-setup queue merges"). The
latter was then reverted by commit ebc69e89 ("Revert "block, bfq:
honor already-setup queue merges""). Yet, the reverted commit was not
the one introducing the bug. In fact, it actually triggered a UAF
introduced by a different commit, and now fixed by commit d29bd414
("block, bfq: reset last_bfqq_created on group change").

So, there is no point in keeping commit 2d52c58b ("block, bfq:
honor already-setup queue merges") out. This commit restores it.

[1] https://bugzilla.kernel.org/show_bug.cgi?id=214503



Reported-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20211125181510.15004-1-paolo.valente@linaro.org


Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Yu Liao <liaoyu15@huawei.com>
Reviewed-by: Wei Li <liwei391@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>