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From: Greg KH <gregkh@linuxfoundation.org>
To: Hugh Dickins <hughd@google.com>
Cc: Peter Xu <peterx@redhat.com>, stable <stable@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>, Igor Raits <igor@gooddata.com>,
	Hillf Danton <hdanton@sina.com>,
	Axel Rasmussen <axelrasmussen@google.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH stable 5.10.y 0/2] mm/thp: Fix uffd-wp with fork(); crash on pmd migration entry on fork
Date: Thu, 22 Jul 2021 16:05:02 +0200	[thread overview]
Message-ID: <YPl7DgqTFzMNNcZA@kroah.com> (raw)
In-Reply-To: <CANsGZ6a6DxnviD3ZPoHCXEEktXguOjNxPuUjjh=v8h0xD3bhvQ@mail.gmail.com>

On Tue, Jul 20, 2021 at 01:38:53PM -0700, Hugh Dickins wrote:
> On Tue, Jul 20, 2021 at 8:57 AM Peter Xu <peterx@redhat.com> 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@google.com/
> >
> > 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@gooddata.com> and
> > debugged by Hugh Dickins <hughd@google.com>.
> >
> > 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.

All now queued up, thanks.

greg k-h

      reply	other threads:[~2021-07-22 14:05 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <796cbb7-5a1c-1ba0-dde5-479aba8224f2@google.com>
2021-07-20 15:51 ` [PATCH stable 5.13.y/5.12.y " Peter Xu
2021-07-20 15:51   ` [PATCH stable 5.13.y/5.12.y 1/2] mm/thp: simplify copying of huge zero page pmd when fork Peter Xu
2021-07-20 15:51   ` [PATCH stable 5.13.y/5.12.y 2/2] mm/userfaultfd: fix uffd-wp special cases for fork() Peter Xu
2021-07-20 20:32   ` [PATCH stable 5.13.y/5.12.y 0/2] mm/thp: Fix uffd-wp with fork(); crash on pmd migration entry on fork Hugh Dickins
2021-07-22 14:02     ` Greg KH
2021-07-20 15:56 ` [PATCH stable 5.10.y " Peter Xu
2021-07-20 15:56   ` [PATCH stable 5.10.y 1/2] mm/thp: simplify copying of huge zero page pmd when fork Peter Xu
2021-07-20 15:56   ` [PATCH stable 5.10.y 2/2] mm/userfaultfd: fix uffd-wp special cases for fork() Peter Xu
2021-07-20 20:38   ` [PATCH stable 5.10.y 0/2] mm/thp: Fix uffd-wp with fork(); crash on pmd migration entry on fork Hugh Dickins
2021-07-22 14:05     ` Greg KH [this message]

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