mm/dynamic_hugetlb: fix list corruption in hpool_merge_page()

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I66OCA


CVE: NA

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The percpu pool will be cleared by clear_percpu_pools(), and then check
whether all pages are already freed. If some pages are not freed, we will
firstly isolate the freed pages and then migrate the used pages.
Since we missed to get lock of percpu_pool, the used pages can be free to
percpu_pool while the isolation is going. In such case, the list operation
will be unreliable.

To fix this problem, we need to get all related locks sequentially and
clear the perpcu_pool again before isolate the freed pages.

Fixes: cdbeee51 ("mm/dynamic_hugetlb: add migration function")
Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Reviewed-by: Tong Tiangen <tongtiangen@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>