Re: runtime regression with "x86/mm/pat: Emulate PAT when it is disabled"

[Paul Gortmaker <paul.gortmaker@windriver.com>]

[Re: runtime regression with "x86/mm/pat: Emulate PAT when it is disabled"] On 04/03/2016 (Fri 15:12) Toshi Kani wrote:

> On Fri, 2016-03-04 at 13:37 -0500, Paul Gortmaker wrote:
> > [Re: runtime regression with "x86/mm/pat: Emulate PAT when it is
> > disabled"] On 03/03/2016 (Thu 22:02) Toshi Kani wrote:
> > 
> > > On Thu, 2016-03-03 at 15:59 -0500, Paul Gortmaker wrote:
>  :
> > > > 
> > > > The stand alone reproducer is here; launched in 00-runme:
> > > > 
> > > > http://openlinux.wrs.com/pat-splat/reproducer.tar.bz2  
> > > > 
> > > > It is nothing fancy, just a generic yocto build of "sato" (gfx
> > > > enabled rootfs).  When it "works" it boots to a UI touchscreen
> > > > interface.  When
> > > > it fails, you get a black screen with a blinking cursor (as seen in
> > > > "vncviewer localhost:0").
> > > 
> > > Thanks for tracking down, and packaging the reproducer.  I simply
> > > untar'd and ran 00-runme, but was not able to connect with localhost:0.
> > >  I am not familiar with qemu, so I have not looked into why, though...
> > 
> > Maybe it was localhost:1 in your case?  The qemu should have indicated
> > what vncserver sessions it started.  Can you paste in the output from
> > the 00-runme?   I tested the reproducer on a machine that was physically
> > distinct from the build, and that was a generic ubuntu install, but with
> > no qemu support installed at all and it worked there.  Plus I got Bruce
> > to test it worked on his machine, so I'm rather surprised it did not
> > work for you.
> 
> I am not really sure what I am doing is correct.
> 
> On one window:
> # ./00-runme
> Warning: vlan 0 is not connected to host network
> VNC server running on '::1:5900'

Ah, it seems for some reason your system confuses qemu from using the
"normal"  IPv4 default.   Try editing ./00-runme and add an explicit
vnc option    "-vnc 127.0.0.1:5" in front of "-show-cursor" and then:

> 
> And another window on the same system:
> # vncviewer localhost:1

...connect to localhost:5  here.  I chose 5 just to not bump into
anything your system might have on :0 or :1 already.

> 
> TigerVNC Viewer 64-bit v1.6.0
> Built on: 2016-01-04 15:09
> Copyright (C) 1999-2015 TigerVNC Team and many others (see README.txt)
> See http://www.tigervnc.org for information on TigerVNC.
> Can't open display: 
> 

[snip analysis, leaving that for Richard to comment on.]

> 
> > > Also, can you send me a whole dmesg output?  I'd like to check how PAT
> > > is initialized.
> > 
> > I'll send the full file off list vs. spamming everyone with it.  I'm open
> > to booting the pre-fail commit with PAT specific bootargs and the post-
> > fail with the same and diffing the two dmesg if there are bootargs you'd
> > like me to test.  I'd also like to ensure you have a working reproducer
> > locally so maybe we should look at how that failed 1st.
> 
> Great.  Yes, two dmesg will be really helpful.

So I booted both with "debugpat" on the bootline; both being the last
working commit [v4.1-rc5-21-g9dac62909451]  and then the 1st failing
commit [v4.1-rc5-22-g9cd25aac1f44].  I captured the dmesg of each, then
stripped the timestamps and diffed them.


--- works.txt	2016-03-06 19:13:28.245836555 -0500
+++ fail.txt	2016-03-06 19:13:17.321836308 -0500
@@ -454,15 +454,38 @@
  8021q: 802.1Q VLAN Support v1.8
  8021q: adding VLAN 0 to HW filter on device eth0
  x86/PAT: Overlap at 0xfd000000-0xfe000000
- x86/PAT: reserve_memtype added [mem 0xfd000000-0xfdffffff], track write-combining, req write-combining, ret write-combining
- x86/PAT: Overlap at 0xfe000000-0xfe010000
- x86/PAT: reserve_memtype added [mem 0xfe000000-0xfe00ffff], track uncached-minus, req uncached-minus, ret uncached-minus
+ x86/PAT: reserve_memtype added [mem 0xfd000000-0xfdffffff], track write-combining, req uncached-minus, ret write-combining
  x86/PAT: free_memtype request [mem 0xfd000000-0xfdffffff]
- x86/PAT: free_memtype request [mem 0xfe000000-0xfe00ffff]
+ x86/PAT: Xorg:475 map pfn expected mapping type uncached-minus for [mem 0xfd000000-0xfdffffff], got write-combining
+ ------------[ cut here ]------------
+ WARNING: CPU: 0 PID: 475 at /home/paul/poky/build/tmp-glibc/work-shared/qemux86/kernel-source/arch/x86/mm/pat.c:938 untrack_pfn+0x9f/0xb0()
+ Modules linked in: 8021q parport_pc parport floppy uvesafb
+ CPU: 0 PID: 475 Comm: Xorg Not tainted 4.1.0-rc5-yocto-standard #1
+ Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.2-0-g33fbe13 by qemu-project.org 04/01/2014
+  00000000 00000000 cdf75db0 c1837711 00000000 cdf75de4 c104f0cb c1a39d10
+  00000000 000001db c1a38f54 000003aa c1049ddf 000003aa c1049ddf 00000000
+  c0108840 00000000 cdf75df4 c104f1a2 00000009 00000000 cdf75e18 c1049ddf
+ Call Trace:
+  [<c1837711>] dump_stack+0x4b/0x75
+  [<c104f0cb>] warn_slowpath_common+0x8b/0xc0
+  [<c1049ddf>] ? untrack_pfn+0x9f/0xb0
+  [<c1049ddf>] ? untrack_pfn+0x9f/0xb0
+  [<c104f1a2>] warn_slowpath_null+0x22/0x30
+  [<c1049ddf>] untrack_pfn+0x9f/0xb0
+  [<c104b9d3>] ? __kunmap_atomic+0x33/0xc0
+  [<c113c07f>] unmap_single_vma+0x49f/0x4b0
+  [<c113cdc3>] unmap_vmas+0x43/0x60
+  [<c11428ff>] exit_mmap+0x5f/0xf0
+  [<c1072d39>] ? get_parent_ip+0x9/0x40
+  [<c104cccd>] mmput+0x2d/0xa0
+  [<c104dfdd>] copy_process.part.45+0x10dd/0x14a0
+  [<c104e541>] do_fork+0xc1/0x390
+  [<c104e8d5>] SyS_clone+0x25/0x30
+  [<c183ef46>] syscall_call+0x7/0x7
+ ---[ end trace dbbf5a6b2dea64ff ]---
  x86/PAT: Overlap at 0xfd000000-0xfe000000
- x86/PAT: reserve_memtype added [mem 0xfd000000-0xfdffffff], track write-combining, req write-combining, ret write-combining
- x86/PAT: Overlap at 0xfe000000-0xfe010000
- x86/PAT: reserve_memtype added [mem 0xfe000000-0xfe00ffff], track uncached-minus, req uncached-minus, ret uncached-minus
+ x86/PAT: reserve_memtype added [mem 0xfd000000-0xfdffffff], track write-combining, req uncached-minus, ret write-combining
  x86/PAT: free_memtype request [mem 0xfd000000-0xfdffffff]
+ x86/PAT: Xorg:475 map pfn expected mapping type uncached-minus for [mem 0xfd000000-0xfdffffff], got write-combining
  x86/PAT: free_memtype request [mem 0xfe000000-0xfe00ffff]
- hrtimer: interrupt took 5057254 ns
+ x86/PAT: free_memtype request [mem 0xfd000000-0xfdffffff]

One obvious difference is the number of overlaps:

~$cat fail.txt |grep Overlap | wc -l
7
~$cat works.txt |grep Overlap | wc -l
9
~$

I'm assuming everyone here is used to reading diffs, but if someone
wants the full dmesg files let me know and I'll send them off-list.

Paul.