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From:   Liam Howlett <liam.howlett@oracle.com>
To:     David Hildenbrand <david@redhat.com>
CC:     Janosch Frank <frankja@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Guenter Roeck <linux@roeck-us.net>,
        "maple-tree@lists.infradead.org" <maple-tree@lists.infradead.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Yu Zhao <yuzhao@google.com>, Juergen Gross <jgross@suse.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Sven Schnelle <svens@linux.ibm.com>,
        Andreas Krebbel <krebbel@linux.ibm.com>,
        Ilya Leoshkevich <iii@linux.ibm.com>,
        Thomas Huth <thuth@redhat.com>
Subject: Re: [PATCH v8 23/70] mm/mmap: change do_brk_flags() to expand
 existing VMA and add do_brk_munmap()
Thread-Topic: [PATCH v8 23/70] mm/mmap: change do_brk_flags() to expand
 existing VMA and add do_brk_munmap()
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Date:   Wed, 4 May 2022 18:47:54 +0000
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* David Hildenbrand <david@redhat.com> [220504 11:31]:
> On 04.05.22 09:37, Janosch Frank wrote:
> > On 5/3/22 23:55, Liam Howlett wrote:
> >> * Heiko Carstens <hca@linux.ibm.com> [220503 15:49]:
> >>> On Mon, May 02, 2022 at 08:50:04PM +0200, Heiko Carstens wrote:
> >>>> On Mon, May 02, 2022 at 01:31:00PM +0000, Liam Howlett wrote:
> >>>>> * Heiko Carstens <hca@linux.ibm.com> [220502 06:18]:
> >>>>>> On Sun, May 01, 2022 at 05:24:12PM -0700, Andrew Morton wrote:
> >>>>>>> (cc S390 maintainers)
> >>>>>>> (cc stable & Greg)
> >>> ...
> >>>>>>>> booting.  The last thing I see is:
> >>>>>>>>
> >>>>>>>> "[    4.668916] Spectre V2 mitigation: execute trampolines"
> >>>>>>>>
> >>>>>>>> I've bisected back to commit e553f62f10d9 (mm, page_alloc: fix
> >>>>>>>> build_zonerefs_node())
> >>>>>>>>
> >>>>>>>> With the this commit, I am unable to boot one out of three times=
.  When
> >>>>>>>> using the previous commit I was not able to get it to hang after=
 trying
> >>>>>>>> 10+ times.  This is a qemu s390 install with KASAN on and I see =
no error
> >>>>>>>> messages.  I think it's likely it is this patch, but no guarante=
ed.
> >>> ...
> >>>>>> Liam, could you share your kernel config?
> >>>>>
> >>>>> Sure thing.  See attached.
> >>>>
> >>>> So, I can reproduce the hanging system now. However this looks like =
a
> >>>> qemu problem on s390, since I can reproduce this only with Qemu+TCG.
> >>>> Qemu with kvm works without any problems (same if I use z/VM as
> >>>> hypervisor).
> >>>>
> >>>> Janosch, Claudio, can you have a look at this please?
> >>>
> >>> So, at least for me this problem also exists with plain v5.17.
> >>> Switching off KASAN, or alternatively switching to KASAN_INLINE
> >>> "fixes" it for me with Qemu+TCG.
> >>>
> >>> Liam, could you please also try to disable KASAN in your config? With
> >>> that I think we can be almost sure this could be some bug in Qemu.
> >>
> >> With KASAN, my tree fails 100% of the time (mm-stable + my maple tree
> >> patches)
> >>
> >> Without KASAN, it boots 100% of the time.
> >>
> >> I think this verifies with you say above?
> >>
> >> Thanks,
> >> Liam
> >=20
> > I had a short look yesterday and the boot usually hangs in the raid6=20
> > code. Disabling vector instructions didn't make a difference but a few=
=20
> > interruptions via GDB solve the problem for some reason.
> >=20
> > CCing David and Thomas for TCG
> >=20
>=20
> I somehow recall that KASAN was always disabled under TCG, I might be
> wrong (I thought we'd get a message early during boot that the HW
> doesn't support KASAN).
>=20
> I recall that raid code is a heavy user of vector instructions.
>=20
> How can I reproduce? Compile upstream (or -next?) with kasan support and
> run it under TCG?

Initially, I found that e553f62f10d9 in mm-stable had this issue.  This
looks to be in v5.18-rc5, at least.

So upstream + kasan should work afaik - but I was using qemu and not
TCG.

Thanks,
Liam=