Re: [PATCH 3/3] s390/mm: fix mis-accounting of pgtable_bytes

[Martin Schwidefsky]

On Tue, 27 Nov 2018 08:34:12 +0100
Heiko Carstens <heiko.carstens@xxxxxxxxxx> wrote:

> On Wed, Oct 31, 2018 at 01:36:23PM +0300, Kirill A. Shutemov wrote:
> > On Wed, Oct 31, 2018 at 11:09:44AM +0100, Heiko Carstens wrote:  
> > > On Wed, Oct 31, 2018 at 07:31:49AM +0100, Martin Schwidefsky wrote:  
> > > > Thanks for testing. Unfortunately Heiko reported another issue yesterday
> > > > with the patch applied. This time the other way around:
> > > > 
> > > > BUG: non-zero pgtables_bytes on freeing mm: -16384
> > > > 
> > > > I am trying to understand how this can happen. For now I would like to
> > > > keep the patch on hold in case they need another change.  
> > > 
> > > FWIW, Kirill: is there a reason why this "BUG:" output is done with
> > > pr_alert() and not with VM_BUG_ON() or one of the WARN*() variants?
> > > 
> > > That would to get more information with DEBUG_VM and / or
> > > panic_on_warn=1 set. At least for automated testing it would be nice
> > > to have such triggers.  
> > 
> > Stack trace is not helpful there. It will always show the exit path which
> > is useless.  
> 
> So, even with the updated version of these patches I can flood dmesg
> and the console with
> 
> BUG: non-zero pgtables_bytes on freeing mm: 16384
> 
> messages with this complex reproducer on s390:
> 
> echo "void main(void) {}" | gcc -m31 -xc -o compat - && ./compat

Forgot a hunk in the fix.. I claim not enough coffee :-/
Patch is queued and I will send a please pull by the end of the week.
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