etmem:fix kasan slab-out-of-bounds in do_swapcache_reclaim

euleros inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5GN7K


CVE: NA

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In the do_swapcache_reclaim interface,
there is a slab-out-of-bounds kasan problem;

The reason for the problem is that when
list_for_each_entry_safe_reverse_from traverses
the LRU linked list, it does not consider that next may be
equal to the head address, which may lead to the
head address being accessed as the page address,
causing problems.

In response to the above problems,
add a judgment about whether pos is head.

Signed-off-by: liubo <liubo254@huawei.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: wangkefeng <wangkefeng.wang@huawei.com>
Signed-off-by: Laibin Qiu <qiulaibin@huawei.com>