On Tue, Jul 20, 2021 at 8:57 AM Peter Xu <peterx@xxxxxxxxxx> wrote: > > In summary, this series should be needed for 5.10/5.12/5.13. This is the 5.10.y > backport of the series. Patch 1 is a dependency of patch 2, while patch 2 > should be the real fix. > > There's a minor conflict on patch 2 when cherry pick due to not having the new > helper called page_needs_cow_for_dma(). It's also mentioned at the entry of > patch 2. > > This series should be able to fix a rare race that mentioned in thread: > > https://lore.kernel.org/linux-mm/796cbb7-5a1c-1ba0-dde5-479aba8224f2@xxxxxxxxxx/ > > This fact wasn't discovered when the fix got proposed and merged, because the > fix was originally about uffd-wp and its fork event. However it turns out that > the problematic commit b569a1760782f3d is also causing crashing on fork() of > pmd migration entries which is even more severe than the original uffd-wp > problem. > > Stable kernels at least on 5.12.y has the crash reproduced, and it's possible > 5.13.y and 5.10.y could hit it due to having the problematic commit > b569a1760782f3d but lacking of the uffd-wp fix patch (8f34f1eac382, which is > also patch 2 of this series). > > The pmd entry crash problem was reported by Igor Raits <igor@xxxxxxxxxxxx> and > debugged by Hugh Dickins <hughd@xxxxxxxxxx>. > > Please review, thanks. And these two for 5.10.y look good to me also: I'm glad you decided in the end to keep 5.10's support for uffd-wp-fork. The first is just a straight cherry-pick of 5fc7a5f6fd04bc18f309d9f979b32ef7d1d0a997, but as you noted above, 8f34f1eac3820fc2722e5159acceb22545b30b0d needed one line of fixup for that tree. Thank you Peter, Hugh > > Peter Xu (2): > mm/thp: simplify copying of huge zero page pmd when fork > mm/userfaultfd: fix uffd-wp special cases for fork() > > include/linux/huge_mm.h | 2 +- > include/linux/swapops.h | 2 ++ > mm/huge_memory.c | 36 +++++++++++++++++------------------- > mm/memory.c | 25 +++++++++++++------------ > 4 files changed, 33 insertions(+), 32 deletions(-) > > -- > 2.31.1 > >
