From: Jan Kara <jack@xxxxxxx> Subject: mm/truncate.c: fix THP handling in invalidate_mapping_pages() The condition checking for THP straddling end of invalidated range is wrong - it checks 'index' against 'end' but 'index' has been already advanced to point to the end of THP and thus the condition can never be true. As a result THP straddling 'end' has been fully invalidated. Given the nature of invalidate_mapping_pages(), this could be only performance issue. In fact, we are lucky the condition is wrong because if it was ever true, we'd leave locked page behind. Fix the condition checking for THP straddling 'end' and also properly unlock the page. Also update the comment before the condition to explain why we decide not to invalidate the page as it was not clear to me and I had to ask Kirill. Link: http://lkml.kernel.org/r/20170619124723.21656-1-jack@xxxxxxx Signed-off-by: Jan Kara <jack@xxxxxxx> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/truncate.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff -puN mm/truncate.c~mm-fix-thp-handling-in-invalidate_mapping_pages mm/truncate.c --- a/mm/truncate.c~mm-fix-thp-handling-in-invalidate_mapping_pages +++ a/mm/truncate.c @@ -530,9 +530,15 @@ unsigned long invalidate_mapping_pages(s } else if (PageTransHuge(page)) { index += HPAGE_PMD_NR - 1; i += HPAGE_PMD_NR - 1; - /* 'end' is in the middle of THP */ - if (index == round_down(end, HPAGE_PMD_NR)) + /* + * 'end' is in the middle of THP. Don't + * invalidate the page as the part outside of + * 'end' could be still useful. + */ + if (index > end) { + unlock_page(page); continue; + } } ret = invalidate_inode_page(page); _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
