From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f70.google.com (mail-pg0-f70.google.com [74.125.83.70]) by kanga.kvack.org (Postfix) with ESMTP id A1A986B0006 for ; Wed, 18 Apr 2018 08:13:06 -0400 (EDT) Received: by mail-pg0-f70.google.com with SMTP id s6so681794pgn.16 for ; Wed, 18 Apr 2018 05:13:06 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id h17sor258321pfn.93.2018.04.18.05.13.05 for (Google Transport Security); Wed, 18 Apr 2018 05:13:05 -0700 (PDT) From: Michal Hocko Subject: [PATCH] mm: Fix do_pages_move status handling Date: Wed, 18 Apr 2018 14:12:55 +0200 Message-Id: <20180418121255.334-1-mhocko@kernel.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Li Wang , Zi Yan , "Kirill A. Shutemov" , ltp@lists.linux.it, linux-mm@kvack.org, LKML , Michal Hocko From: Michal Hocko Li Wang has reported that LTP move_pages04 test fails with the current tree: LTP move_pages04: TFAIL : move_pages04.c:143: status[1] is EPERM, expected EFAULT The test allocates an array of two pages, one is present while the other is not (resp. backed by zero page) and it expects EFAULT for the second page as the man page suggests. We are reporting EPERM which doesn't make any sense and this is a result of a bug from cf5f16b23ec9 ("mm: unclutter THP migration"). do_pages_move tries to handle as many pages in one batch as possible so we queue all pages with the same node target together and that corresponds to [start, i] range which is then used to update status array. add_page_for_migration will correctly notice the zero (resp. !present) page and returns with EFAULT which gets written to the status. But if this is the last page in the array we do not update start and so the last store_status after the loop will overwrite the range of the last batch with NUMA_NO_NODE (which corresponds to EPERM). Fix this by simply bailing out from the last flush if the pagelist is empty as there is clearly nothing more to do. Fixes: cf5f16b23ec9 ("mm: unclutter THP migration") Reported-and-Tested-by: Li Wang Signed-off-by: Michal Hocko --- Hi Andrew, this is a new regression in 4.17-rc1 so it would be great to merge sooner rather than later. It is a user visible change. The original bug report is http://lkml.kernel.org/r/20180417110615.16043-1-liwang@redhat.com Thanks to Li Wang for his testing! mm/migrate.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/mm/migrate.c b/mm/migrate.c index 507cf9ba21bf..c7e5f6447417 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1634,6 +1634,9 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes, current_node = NUMA_NO_NODE; } out_flush: + if (list_empty(&pagelist)) + return err; + /* Make sure we do not overwrite the existing error */ err1 = do_move_pages_to_node(mm, &pagelist, current_node); if (!err1) -- 2.16.3