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Thu, 22 Jul 2021 10:02:22 -0400 (EDT) Date: Thu, 22 Jul 2021 16:02:18 +0200 From: Greg KH To: Hugh Dickins Cc: Peter Xu , stable , linux-mm , linux-kernel , Axel Rasmussen , Andrew Morton , Hillf Danton , Igor Raits Subject: Re: [PATCH stable 5.13.y/5.12.y 0/2] mm/thp: Fix uffd-wp with fork(); crash on pmd migration entry on fork Message-ID: References: <796cbb7-5a1c-1ba0-dde5-479aba8224f2@google.com> <20210720155150.497148-1-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=kroah.com header.s=fm1 header.b="cn/4EYJ/"; dkim=pass header.d=messagingengine.com header.s=fm3 header.b=JctVrWUE; spf=pass (imf13.hostedemail.com: domain of greg@kroah.com designates 64.147.123.17 as permitted sender) smtp.mailfrom=greg@kroah.com; dmarc=none X-Stat-Signature: 9q8x1a7irxz5car8s6ugsycodps3kxwx X-Rspamd-Queue-Id: F1DB4100FBF7 X-Rspamd-Server: rspam01 X-HE-Tag: 1626962546-956891 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Jul 20, 2021 at 01:32:19PM -0700, Hugh Dickins wrote: > On Tue, Jul 20, 2021 at 8:52 AM Peter Xu 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@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 and > > debugged by Hugh Dickins . > > > > 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@vger.kernel.org to > cherry-pick the two commits > 5fc7a5f6fd04bc18f309d9f979b32ef7d1d0a997 > 8f34f1eac3820fc2722e5159acceb22545b30b0d Thanks for the review, both now queued up to 5.13.y. greg k-h