mm, hugetlb, soft_offline: save compound page order before page migration

This fixes a bug in madvise() where if you'd try to soft offline a
hugepage via madvise(), while walking the address range you'd end up,
using the wrong page offset due to attempting to get the compound order
of a former but presently not compound page, due to dissolving the huge
page (since commit c3114a84f7f9: "mm: hugetlb: soft-offline: dissolve
source hugepage after successful migration").

As a result I ended up with all my free pages except one being offlined.

Link: http://lkml.kernel.org/r/20170912204306.GA12053@gmail.com
Fixes: c3114a84f7f9 ("mm: hugetlb: soft-offline: dissolve source hugepage after successful migration")
Signed-off-by: Alexandru Moise <00moses.alexander00@gmail.com>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Shaohua Li <shli@fb.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/madvise.c b/mm/madvise.c
index 21261ff..25bade3 100644 (file)
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -625,18 +625,26 @@ static int madvise_inject_error(int behavior,
 {
        struct page *page;
        struct zone *zone;
+       unsigned int order;
 
        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;
 
-       for (; start < end; start += PAGE_SIZE <<
-                               compound_order(compound_head(page))) {
+
+       for (; start < end; start += PAGE_SIZE << order) {
                int ret;
 
                ret = get_user_pages_fast(start, 1, 0, &page);
                if (ret != 1)
                        return ret;
 
+               /*
+                * When soft offlining hugepages, after migrating the page
+                * we dissolve it, therefore in the second loop "page" will
+                * no longer be a compound page, and order will be 0.
+                */
+               order = compound_order(compound_head(page));
+
                if (PageHWPoison(page)) {
                        put_page(page);
                        continue;