On Tue 21 Nov 2017, 17:35, Zi Yan wrote: > On 21 Nov 2017, at 17:12, Andrew Morton wrote: > > > On Mon, 20 Nov 2017 21:18:55 -0500 Zi Yan <[email protected]> wrote: > > > >> This patch fixes it by only calling prep_transhuge_page() when we are > >> certain that the target page is THP. > > > > What are the user-visible effects of the bug? > > 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.
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. Best, Andrea
