Date:	Tue, 21 Jan 2014 23:29:14 -0800
From:	Steven Noonan <steven@...inklabs.net>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	boris.ostrovsky@...cle.com, david.vrabel@...rix.com,
	xen-devel@...ts.xenproject.org, george.dunlap@...citrix.com,
	dario.faggioli@...rix.com, Elena Ufimtseva <ufimtseva@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Linux Kernel mailing List <linux-kernel@...r.kernel.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Alex Thorlton <athorlton@....com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [BISECTED] Linux 3.12.7 introduces page map handling regression

On Wed, Jan 22, 2014 at 12:02:15AM -0500, Konrad Rzeszutek Wilk wrote:
> On Tue, Jan 21, 2014 at 07:20:45PM -0800, Steven Noonan wrote:
> > On Tue, Jan 21, 2014 at 06:47:07PM -0800, Linus Torvalds wrote:
> > > On Tue, Jan 21, 2014 at 5:49 PM, Greg Kroah-Hartman
> > > <gregkh@...uxfoundation.org> wrote:
> 
> Adding extra folks to the party.
> > > >
> > > > Odds are this also shows up in 3.13, right?
> > 
> > Reproduced using 3.13 on the PV guest:
> > 
> > 	[  368.756763] BUG: Bad page map in process mp  pte:80000004a67c6165 pmd:e9b706067
> > 	[  368.756777] page:ffffea001299f180 count:0 mapcount:-1 mapping:          (null) index:0x0
> > 	[  368.756781] page flags: 0x2fffff80000014(referenced|dirty)
> > 	[  368.756786] addr:00007fd1388b7000 vm_flags:00100071 anon_vma:ffff880e9ba15f80 mapping:          (null) index:7fd1388b7
> > 	[  368.756792] CPU: 29 PID: 618 Comm: mp Not tainted 3.13.0-ec2 #1
> > 	[  368.756795]  ffff880e9b718958 ffff880e9eaf3cc0 ffffffff814d8748 00007fd1388b7000
> > 	[  368.756803]  ffff880e9eaf3d08 ffffffff8116d289 0000000000000000 0000000000000000
> > 	[  368.756809]  ffff880e9b7065b8 ffffea001299f180 00007fd1388b8000 ffff880e9eaf3e30
> > 	[  368.756815] Call Trace:
> > 	[  368.756825]  [<ffffffff814d8748>] dump_stack+0x45/0x56
> > 	[  368.756833]  [<ffffffff8116d289>] print_bad_pte+0x229/0x250
> > 	[  368.756837]  [<ffffffff8116eae3>] unmap_single_vma+0x583/0x890
> > 	[  368.756842]  [<ffffffff8116feb5>] unmap_vmas+0x65/0x90
> > 	[  368.756847]  [<ffffffff81175dac>] unmap_region+0xac/0x120
> > 	[  368.756852]  [<ffffffff81176379>] ? vma_rb_erase+0x1c9/0x210
> > 	[  368.756856]  [<ffffffff81177f10>] do_munmap+0x280/0x370
> > 	[  368.756860]  [<ffffffff81178041>] vm_munmap+0x41/0x60
> > 	[  368.756864]  [<ffffffff81178f32>] SyS_munmap+0x22/0x30
> > 	[  368.756869]  [<ffffffff814e70ed>] system_call_fastpath+0x1a/0x1f
> > 	[  368.756872] Disabling lock debugging due to kernel taint
> > 	[  368.760084] BUG: Bad rss-counter state mm:ffff880e9d079680 idx:0 val:-1
> > 	[  368.760091] BUG: Bad rss-counter state mm:ffff880e9d079680 idx:1 val:1
> > 
> > > 
> > > Probably. I don't have a Xen PV setup to test with (and very little
> > > interest in setting one up).. And I have a suspicion that it might not
> > > be so much about Xen PV, as perhaps about the kind of hardware.
> > > 
> > > I suspect the issue has something to do with the magic _PAGE_NUMA
> > > tie-in with _PAGE_PRESENT. And then mprotect(PROT_NONE) ends up
> > > removing the _PAGE_PRESENT bit, and now the crazy numa code is
> > > confused.
> > > 
> > > The whole _PAGE_NUMA thing is a f*cking horrible hack, and shares the
> > > bit with _PAGE_PROTNONE, which is why it then has that tie-in to
> > > _PAGE_PRESENT.
> > > 
> > > Adding Andrea to the Cc, because he's the author of that horridness.
> > > Putting Steven's test-case here as an attachement for Andrea, maybe
> > > that makes him go "Ahh, yes, silly case".
> > > 
> > > Also added Kirill, because he was involved the last _PAGE_NUMA debacle.
> > > 
> > > Andrea, you can find the thread on lkml, but it boils down to commit
> > > 1667918b6483 (backported to 3.12.7 as 3d792d616ba4) breaking the
> > > attached test-case (but apparently only under Xen PV). There it
> > > apparently causes a "BUG: Bad page map .." error.
> 
> I *think* it is due to the fact that pmd_numa and pte_numa is getting the _raw_
> value of PMDs and PTEs. That is - it does not use the pvops interface
> and instead reads the values directly from the page-table. Since the
> page-table is also manipulated by the hypervisor - there are certain
> flags it also sets to do its business. It might be that it uses
> _PAGE_GLOBAL as well - and Linux picks up on that. If it was using
> pte_flags that would invoke the pvops interface.
> 
> Elena, Dariof and George, you guys had been looking at this a bit deeper
> than I have. Does the Xen hypervisor use the _PAGE_GLOBAL for PV guests?
> 
> This not-compiled-totally-bad-patch might shed some light on what I was
> thinking _could_ fix this issue - and IS NOT A FIX - JUST A HACK.
> It does not fix it for PMDs naturally (as there are no PMD paravirt ops
> for that).

Unfortunately the Totally Bad Patch seems to make no difference. I am
still able to repro the issue:

	[  346.374929] BUG: Bad page map in process mp  pte:80000004ae928065 pmd:e993f9067
	[  346.374942] page:ffffea0012ba4a00 count:0 mapcount:-1 mapping:          (null) index:0x0
	[  346.374946] page flags: 0x2fffff80000014(referenced|dirty)
	[  346.374951] addr:00007f06a9bbb000 vm_flags:00100071 anon_vma:ffff880e9939fe00 mapping:          (null) index:7f06a9bbb
	[  346.374956] CPU: 29 PID: 609 Comm: mp Not tainted 3.13.0-ec2+ #1
	[  346.374960]  ffff880e9cc38da8 ffff880e991a3cc0 ffffffff814d8768 00007f06a9bbb000
	[  346.374967]  ffff880e991a3d08 ffffffff8116d289 0000000000000000 0000000000000000
	[  346.374972]  ffff880e993f9dd8 ffffea0012ba4a00 00007f06a9bbc000 ffff880e991a3e30
	[  346.374979] Call Trace:
	[  346.374988]  [<ffffffff814d8768>] dump_stack+0x45/0x56
	[  346.374996]  [<ffffffff8116d289>] print_bad_pte+0x229/0x250
	[  346.375000]  [<ffffffff8116eae3>] unmap_single_vma+0x583/0x890
	[  346.375006]  [<ffffffff8116feb5>] unmap_vmas+0x65/0x90
	[  346.375011]  [<ffffffff81175dbc>] unmap_region+0xac/0x120
	[  346.375016]  [<ffffffff81176389>] ? vma_rb_erase+0x1c9/0x210
	[  346.375021]  [<ffffffff81177f20>] do_munmap+0x280/0x370
	[  346.375025]  [<ffffffff81178051>] vm_munmap+0x41/0x60
	[  346.375029]  [<ffffffff81178f42>] SyS_munmap+0x22/0x30
	[  346.375034]  [<ffffffff814e712d>] system_call_fastpath+0x1a/0x1f
	[  346.375037] Disabling lock debugging due to kernel taint
	[  346.380082] BUG: Bad rss-counter state mm:ffff880e9d22bc00 idx:0 val:-1
	[  346.380088] BUG: Bad rss-counter state mm:ffff880e9d22bc00 idx:1 val:1

This dump doesn't look dramatically different, either.

> 
> The other question is - how is AutoNUMA running when it is not enabled?
> Shouldn't those _PAGE_NUMA ops be nops when AutoNUMA hasn't even been
> turned on?

Well, NUMA_BALANCING is enabled in the kernel config[1], but I presume you
mean not enabled at runtime?

[1] http://git.uplinklabs.net/snoonan/projects/archlinux/ec2/ec2-packages.git/tree/linux-ec2/config.x86_64

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