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From:   Yu Zhao <yuzhao@google.com>
Date:   Mon, 23 May 2022 14:56:12 -0600
Message-ID: <CAOUHufZ_kBF+f3_RE9p8itJ8YN86cbEq9oXHCt+e1qw2Q-b8Zw@mail.gmail.com>
Subject: Re: Alpha: rare random memory corruption/segfault in user space bisected
To:     Michael Cree <mcree@orcon.net.nz>
Cc:     Linux-MM <linux-mm@kvack.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Hillf Danton <hdanton@sina.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>
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On Wed, May 11, 2022 at 2:37 PM Michael Cree <mcree@orcon.net.nz> wrote:
>
> On Sat, May 07, 2022 at 11:27:15AM -0700, Yu Zhao wrote:
> > On Fri, May 6, 2022 at 6:57 PM Hillf Danton <hdanton@sina.com> wrote:
> > >
> > > On Sat, 7 May 2022 09:21:25 +1200 Michael Cree wrote:
> > > > Alpha kernel has been exhibiting rare and random memory
> > > > corruptions/segaults in user space since the 5.9.y kernel.  First seen
> > > > on the Debian Ports build daemon when running 5.10.y kernel resulting
> > > > in the occasional (one or two a day) build failures with gcc ICEs either
> > > > due to self detected corrupt memory structures or segfaults.  Have been
> > > > running 5.8.y kernel without such problems for over six months.
> > > >
> > > > Tried bisecting last year but went off track with incorrect good/bad
> > > > determinations due to rare nature of bug.  After trying a 5.16.y kernel
> > > > early this year and seen the bug is still present retried the bisection
> > > > and have got to:
> > > >
> > > > aae466b0052e1888edd1d7f473d4310d64936196 is the first bad commit
> > > > commit aae466b0052e1888edd1d7f473d4310d64936196
> > > > Author: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> > > > Date:   Tue Aug 11 18:30:50 2020 -0700
> > > >
> > > >     mm/swap: implement workingset detection for anonymous LRU
> >
> > This commit seems innocent to me. While not ruling out anything, i.e.,
> > this commit, compiler, qemu, userspace itself, etc., my wild guess is
> > the problem is memory barrier related. Two lock/unlock pairs, which
> > imply two full barriers, were removed. This is not a small deal on
> > Alpha, since it imposes no constraints on cache coherency, AFAIK.
> >
> > Can you please try the attached patch on top of this commit? Thanks!
>
> Thanks, I have that running now for a day without any problem showing
> up, but that's not long enough to be sure it has fixed the problem. Will
> get back to you after another day or two of testing.

Any luck? Thanks!