[PATCH v8 23/70] mm/mmap: change do_brk_flags() to expand existing VMA and add do_brk_munmap()

David Hildenbrand david at redhat.com
Wed May 4 11:31:22 PDT 2022

On 04.05.22 09:37, Janosch Frank wrote:
> On 5/3/22 23:55, Liam Howlett wrote:
>> * Heiko Carstens <hca at 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 at 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 guaranteed.
>>> ...
>>>>>> 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
> I had a short look yesterday and the boot usually hangs in the raid6 
> code. Disabling vector instructions didn't make a difference but a few 
> interruptions via GDB solve the problem for some reason.
> CCing David and Thomas for TCG

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).

I recall that raid code is a heavy user of vector instructions.

How can I reproduce? Compile upstream (or -next?) with kasan support and
run it under TCG?


David / dhildenb

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