Re: mmotm 2015-01-22-15-04: qemu failures due to 'mm: account pmd page tables to the process'

[Guenter Roeck]

On 01/26/2015 06:03 AM, Guenter Roeck wrote:
> On 01/26/2015 04:29 AM, Kirill A. Shutemov wrote:
> > On Fri, Jan 23, 2015 at 09:52:07PM -0800, Guenter Roeck wrote:
> > > On Fri, Jan 23, 2015 at 01:55:19PM -0800, Andrew Morton wrote:
> > > > On Fri, 23 Jan 2015 07:07:56 -0800 Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > > >
> > > > > > > qemu:microblaze generates warnings to the console.
> > > > > > >
> > > > > > > WARNING: CPU: 0 PID: 32 at mm/mmap.c:2858 exit_mmap+0x184/0x1a4()
> > > > > > >
> > > > > > > with various call stacks. See
> > > > > > > http://server.roeck-us.net:8010/builders/qemu-microblaze-mmotm/builds/15/steps/qemubuildcommand/logs/stdio
> > > > > > > for details.
> > > > > >
> > > > > > Could you try patch below? Completely untested.
> > > > > >
> > > > > > >From b584bb8d493794f67484c0b57c161d61c02599bc Mon Sep 17 00:00:00 2001
> > > > > > From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> > > > > > Date: Fri, 23 Jan 2015 13:08:26 +0200
> > > > > > Subject: [PATCH] microblaze: define __PAGETABLE_PMD_FOLDED
> > > > > >
> > > > > > Microblaze uses custom implementation of PMD folding, but doesn't define
> > > > > > __PAGETABLE_PMD_FOLDED, which generic code expects to see. Let's fix it.
> > > > > >
> > > > > > Defining __PAGETABLE_PMD_FOLDED will drop out unused __pmd_alloc().
> > > > > > It also fixes problems with recently-introduced pmd accounting.
> > > > > >
> > > > > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > > > > > Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > > > >
> > > > > Tested working.
> > > > >
> > > > > Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > > > >
> > > > > Any idea how to fix the sh problem ?
> > > >
> > > > Can you tell us more about it?  All I'm seeing is "qemu:sh fails to
> > > > shut down", which isn't very clear.
> > >
> > > Turns out that the include file defining __PAGETABLE_PMD_FOLDED
> > > was not always included where used, resulting in a messed up mm_struct.
> >
> > What means "messed up" here? It should only affect size of mm_struct.
> Plus the offset of all variables after the #ifndef.
>
> > > The patch below fixes the problem for the sh architecture.
> > > No idea if the patch is correct/acceptable for other architectures.
> >
> > That's pain. Some archs includes <linux/mm_types.h> from <asm/pgtable.h>.
> > I don't see obvious way to fix this. Urghh.
> Does it matter ? Circular includes are normally ok and happen all over the place.

Ah yes, it does, because mm_struct will not see the define in that case
since it comes later. Hmm, that is really tricky. You could of course
just drop the conditional from mm_struct. That would result in an unused
variable for some architectures, but at least it would work.

Guenter

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