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

[Liam Howlett]

* 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