On Mon, Jan 13, 2020 at 01:57:18AM +0300, Kirill A. Shutemov wrote: >On Sun, Jan 12, 2020 at 10:28:58AM +0800, Wei Yang wrote: >> On Sat, Jan 11, 2020 at 03:03:52AM +0300, Kirill A. Shutemov wrote: >> >On Thu, Jan 09, 2020 at 10:30:54PM +0800, Wei Yang wrote: >> >> As all the other places, we grab the lock before manipulate the defer list. >> >> Current implementation may face a race condition. >> >> >> >> For example, the potential race would be: >> >> >> >> CPU1 CPU2 >> >> mem_cgroup_move_account split_huge_page_to_list >> >> !list_empty >> >> lock >> >> !list_empty >> >> list_del >> >> unlock >> >> lock >> >> # !list_empty might not hold anymore >> >> list_del_init >> >> unlock >> > >> >I don't think this particular race is possible. Both parties take page >> >lock before messing with deferred queue, but anytway: >> >> I am afraid not. Page lock is per page, while defer queue is per pgdate or >> memcg. >> >> It is possible two page in the same pgdate or memcg grab page lock >> respectively and then access the same defer queue concurrently. > >Look closer on the list_empty() argument. It's list_head local to the >page. Too different pages can be handled in parallel without any problem >in this particular scenario. As long as we as we modify it under the lock. > >Said that, page lock here was somewhat accidential and I still belive we >need to move the check under the lock anyway. > If my understanding is correct, you agree with my statement? >-- > Kirill A. Shutemov -- Wei Yang Help you, Help me
