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: 8135d892 ("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>
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