mm/z3fold: always clear PAGE_CLAIMED under z3fold page lock

mm/z3fold: always clear PAGE_CLAIMED under z3fold page lock

Think about the below race window:

CPU1				CPU2
z3fold_reclaim_page		z3fold_free
 test_and_set_bit PAGE_CLAIMED
 failed to reclaim page
 z3fold_page_lock(zhdr);
 add back to the lru list;
 z3fold_page_unlock(zhdr);
				 get_z3fold_header
				 page_claimed=test_and_set_bit PAGE_CLAIMED

 clear_bit(PAGE_CLAIMED, &page->private);

				 if (!page_claimed) /* it's false true */
				  free_handle is not called

free_handle won't be called in this case. So z3fold_buddy_slots will leak.
Fix it by always clear PAGE_CLAIMED under z3fold page lock.

Link: https://lkml.kernel.org/r/20220429064051.61552-8-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>