lkml.org 
[lkml]   [2019]   [Nov]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRe: [PATCH v5 1/2] mm,thp: recheck each page before collapsing file THP
    Date

    > On Nov 5, 2019, at 10:09 PM, Song Liu <songliubraving@fb.com> 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. The only case we hit a dirty page here is
    > when the page hasn't been written since write. Bail out and retry when
    > this happens.
    >
    > syzbot reported bug on previous version of this patch.
    >
    > Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
    > Reported-by: syzbot+efb9e48b9fbdc49bb34a@syzkaller.appspotmail.com
    > Cc: Johannes Weiner <hannes@cmpxchg.org>
    > Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    > 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>

    I think we need this in 5.4 official, but I haven't seen it in Linus'
    master branch.

    Hi Andrew,

    Could you please send patch/pull-request for it?

    Thanks,
    Song
    \
     
     \ /
      Last update: 2019-11-14 00:48    [W:5.103 / U:0.008 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site