hwpoison_user_mappings() is updated to support ksm pages, and addReviewed-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
collect_procs_ksm() to collect processes when the error hit an ksm
page. The difference from collect_procs_anon() is that it also needs
to traverse the rmap-item list on the stable node of the ksm page.
At the same time, add_to_kill_ksm() is added to handle ksm pages. And
task_in_to_kill_list() is added to avoid duplicate addition of tsk to
the to_kill list. This is because when scanning the list, if the pages
that make up the ksm page all come from the same process, they may be
added repeatedly.