On Tue, Jul 20, 2021 at 01:32:19PM -0700, Hugh Dickins wrote: > On Tue, Jul 20, 2021 at 8:52 AM Peter Xu <peterx@xxxxxxxxxx> wrote: > > > > In summary: this series should be needed for 5.10/5.12/5.13. This is the > > 5.13.y/5.12.y backport of the series, and it should be able to be applied on > > both of the branches. Patch 1 is a dependency of patch 2, while patch 2 should > > be the real fix. > > > > 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. > > These two 5.13.y patches look just right to me, thank you Peter (and > 5.12.19 announced EOL overnight, so nothing more wanted for that). > > But these do just amount to asking stable@xxxxxxxxxxxxxxx to > cherry-pick the two commits > 5fc7a5f6fd04bc18f309d9f979b32ef7d1d0a997 > 8f34f1eac3820fc2722e5159acceb22545b30b0d Thanks for the review, both now queued up to 5.13.y. greg k-h
