Re: [BISECTED] Linux 3.12.7 introduces page map handling regression

From: Daniel Borkmann
Date: Wed Jan 22 2014 - 09:30:22 EST

On 01/22/2014 08:29 AM, Steven Noonan wrote:
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@xxxxxxxxxxxxxxxxxxx> 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:

Maybe this one is also related to this BUG here (cc'ed people investigating
this one) ...

https://lkml.org/lkml/2014/1/10/427

... not sure, though.

[ 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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