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

[Heiko Carstens <hca@linux.ibm.com>]

On Sun, May 01, 2022 at 05:24:12PM -0700, Andrew Morton wrote:
> (cc S390 maintainers)
> (cc stable & Greg)
> 
> > I have been porting my patches over and hit a bit of a snag. It looked
> > like my patches were not booting on the s390 - but not all the time. So
> > I reverted back to mm-stable (059342d1dd4e) and found that also failed
> > to boot sometimes on my qemu setup.  When it fails it's ~4-5sec into
> > 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.
> > 
> 
> Great, thanks.  So mapletree is absolved.
> 
> Unfortunately 059342d1dd4e was cc:stable.  Greg, you might want to pull
> the plug on that one if it isn't too late.
> 
> I'll await input from the S390 team, but from my reading the issues
> which that patch addresses aren't terribly serious, so perhaps the
> thing to do is to revert 059342d1dd4e (with a cc:stable) while
> 059342d1dd4e gets a redo?

I cannot confirm that Linus' tree currently has problems on s390 with
commit e553f62f10d9 ("mm, page_alloc: fix build_zonerefs_node()").

This commit was applied by Linus on 15th of April, and our CI didn't
report any problems since then. At least nothing that would point to
this commit. Also I just gave e553f62f10d9 a try (defconfig + KASAN):
no problems to report.

Same with 059342d1dd4e (mm-stable): it just works for me.

Liam, could you share your kernel config?