mm: migrate: fix an incorrect call of prep_transhuge_page()
In https://lkml.org/lkml/2017/11/20/411, Andrea reported that during
memory hotplug/hot remove prep_transhuge_page() is called incorrectly on
non-THP pages for migration, when THP is on but THP migration is not
enabled. This leads to a bad state of target pages for migration.
By inspecting the code, if called on a non-THP, prep_transhuge_page()
will
1) change the value of the mapping of (page + 2), since it is used for
THP deferred list;
2) change the lru value of (page + 1), since it is used for THP's dtor.
Both can lead to data corruption of these two pages.
Andrea said:
"Pragmatically and from the point of view of the memory_hotplug subsys,
the effect is a kernel crash when pages are being migrated during a
memory hot remove offline and migration target pages are found in a
bad state"
This patch fixes it by only calling prep_transhuge_page() when we are
certain that the target page is THP.
Link: http://lkml.kernel.org/r/20171121021855.50525-1-zi.yan@sent.com
Fixes: 8135d8926c08 ("mm: memory_hotplug: memory hotremove supports thp migration")
Signed-off-by: Zi Yan <zi.yan@cs.rutgers.edu>
Reported-by: Andrea Reale <ar@linux.vnet.ibm.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: "Jérôme Glisse" <jglisse@redhat.com>
Cc: <stable@vger.kernel.org> [4.14]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 895ec0c..a2246cf 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -54,7 +54,7 @@
new_page = __alloc_pages_nodemask(gfp_mask, order,
preferred_nid, nodemask);
- if (new_page && PageTransHuge(page))
+ if (new_page && PageTransHuge(new_page))
prep_transhuge_page(new_page);
return new_page;