Messages in this thread | | | Date | Mon, 21 Oct 2019 14:03:14 -0400 | From | Johannes Weiner <> | Subject | Re: [PATCH v3] mm,thp: recheck each page before collapsing file THP |
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On Sat, Oct 19, 2019 at 05:24:00AM +0000, Song Liu wrote: > In collapse_file(), for !is_shmem case, current check cannot guarantee > the locked page is up-to-date. Specifically, xas_unlock_irq() should not > be called before lock_page() and get_page(); and it is necessary to > recheck PageUptodate() after locking the page. > > With this bug and CONFIG_READ_ONLY_THP_FOR_FS=y, madvise(HUGE)'ed .text > may contain corrupted data. This is because khugepaged mistakenly > collapses some not up-to-date sub pages into a huge page, and assumes the > huge page is up-to-date. This will NOT corrupt data in the disk, because > the page is read-only and never written back. Fix this by properly > checking PageUptodate() after locking the page. This check replaces > "VM_BUG_ON_PAGE(!PageUptodate(page), page);". > > Also, move PageDirty() check after locking the page. Current khugepaged > should not try to collapse dirty file THP, because it is limited to > read-only .text. Add a warning with the PageDirty() check as it should > not happen. This warning is added after page_mapping() check, because > if the page is truncated, it might be dirty. > > Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS") > Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > Cc: Johannes Weiner <hannes@cmpxchg.org> > Cc: Hugh Dickins <hughd@google.com> > Cc: William Kucharski <william.kucharski@oracle.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Signed-off-by: Song Liu <songliubraving@fb.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
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