Re: [PATCH] mm: don't overwrite mm->def_flags in do_mlockall()

Gerald Schaefer
2013-02-07T12:59:28Z

On Wed, 6 Feb 2013 12:51:03 -0800
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Wed, 6 Feb 2013 16:49:34 +0100
> Gerald Schaefer <gerald.schaefer@de.ibm.com> wrote:
>
> > With commit 8e72033 "thp: make MADV_HUGEPAGE check for
> > mm->def_flags" the VM_NOHUGEPAGE flag may be set on s390 in
> > mm->def_flags for certain processes, to prevent future thp
> > mappings. This would be overwritten by do_mlockall(), which sets it
> > back to 0 with an optional VM_LOCKED flag set.
> >
> > To fix this, instead of overwriting mm->def_flags in do_mlockall(),
> > only the VM_LOCKED flag should be set or cleared.
>
> What are the user-visible effects here? Looking at the 274023da1e8
> changelog, I'm guessing that it might be pretty nasty - kvm breakage?

Yes, though at the moment there should be no mlockall()/munlockall()
involved with kvm/qemu. So currently no user-visible effects, Vivek
found this while reading the do_mlockall() code, but it might be a
good idea to add this to stable.
Could you add a "Cc: stable@vger.kernel.org # v3.7+"?

Thanks,
Gerald