| Message ID | 20170601093245.29238-6-jack@suse.cz (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
diff --git a/mm/truncate.c b/mm/truncate.c index 6479ed2afc53..2330223841fb 100644 --- a/mm/truncate.c +++ b/mm/truncate.c @@ -530,9 +530,15 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping, } 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);
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. Signed-off-by: Jan Kara <jack@suse.cz> --- mm/truncate.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)