ksm: revert "use GET_KSM_PAGE_NOLOCK to get ksm page in remove_rmap_item_from_tree()"

ksm: revert "use GET_KSM_PAGE_NOLOCK to get ksm page in remove_rmap_item_from_tree()"

This reverts commit 3057d8b41693b4f30e5e055bcedd178844c2d260.  General
Protection Fault in rmap_walk_ksm() under memory pressure:
remove_rmap_item_from_tree() needs to take page lock, of course.

Link: https://lkml.kernel.org/r/alpine.LSU.2.11.2105092253500.1127@eggly.anvils
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>