blk-throtl: fix race in io dispatching

hulk inclusion
category: bugfix
bugzilla: 186449, https://gitee.com/openeuler/kernel/issues/I4YSPC


CVE: NA

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If io is throttled, such io will be issued by blk_throtl_dispatch_work_fn()
or blk_throtl_drain(), and the io is fetched by throtl_pop_queued().
throtl_pop_queued() should be protected by 'queue_lock', as what
blk_throtl_dispatch_work_fn() does. However, it's not protected in
blk_throtl_drain(), which may lead to concurrent bio_list_pop(), and may
end up crashing the kernel.

Fix the problem by protecting throtl_pop_queued() through 'queue_lock'
in blk_throtl_drain().

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>