On 21 Nov 2017, at 17:12, Andrew Morton wrote: > On Mon, 20 Nov 2017 21:18:55 -0500 Zi Yan <zi.yan@xxxxxxxx> wrote: > >> In [1], 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. >> >> 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. — Best Regards, Yan Zi
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