Date:	Fri, 9 May 2008 12:28:32 -0300
From:	"Glauber Costa" <glommer@...il.com>
To:	"Hugh Dickins" <hugh@...itas.com>
Cc:	"Theodore Ts'o" <tytso@....edu>,
	"Glauber Costa" <gcosta@...hat.com>, "Ingo Molnar" <mingo@...e.hu>,
	linux-kernel@...r.kernel.org
Subject: Re: Possible regression? 2.6.26-rc1: T61s failure after suspend/resume

On Thu, May 8, 2008 at 6:48 PM, Hugh Dickins <hugh@...itas.com> wrote:
> On Thu, 8 May 2008, Theodore Ts'o wrote:
>  >
>  > I'm running a kernel based off of commit afa26be8 (just six commits
>  > after 2.6.26-rc1), and very shortly after I suspend/resume my X61s (with
>  > the Intel video chipset), the X server will lock up.  I can ssh into
>  > the machine remotely, and restart the X server, but the newly restarted
>  > X server will shortly lock up again, and the only way to solve the
>  > problem is to reboot.  If I drop back to a 2.6.25 based kernel, the
>  > problem goes away.
>  >
>  > I've tried bisecting it, but the bisection points picked by git don't
>  > boot at all, and given that I'm travelling I havent had much time to try
>  > doing more bisecting; since I know a number of kernel developers have
>  > Lenovo X61 laptops, I thought before I wasted more time trying to get
>  > the git bisection to work, I'd check to see if anyone has seen this
>  > problem and if the fix is known.  I'll also try the latest bleeding edge
>  > kernel and hope it's fixed there....
>
>  I don't have a Lenovo X61, and I've no problem on my uniprocessor T43p.
>  But I also have a Fujitsu Siemens Esprimo Mobile, Core2 Duo and Intel
>  graphics like yours, and that's been behaving strangely after resume
>  from RAM since somewhere between 2.6.25 and 2.6.26-rc1.
>
>  Sounds like it might be the same problem, though I quickly moved away
>  trying it with X, and have been trying to investigate just from the
>  console for some days now.  Weird memory corruption after resume.
>
>  Like you, little success with bisection: probably-other bugs get in
>  the way.  Some bisection points don't boot, some don't come back from
>  resume at all, some hang before getting to test.  When, as a working
>  hypothesis, I assumed that not coming back from resume might be the
>  same problem manifesting in the return from resume itself, and shifted
>  around bisection points a bit to avoid non-booting, then it arrived at
>
>  commit 4fe29a85642544503cf81e9cf251ef0f4e65b162
>  Author: Glauber de Oliveira Costa <gcosta@...hat.com>
>  Date:   Wed Mar 19 14:25:23 2008 -0300
>     x86: use specialized routine for setup per-cpu area
>
>  as the suspect commit.  But I couldn't see anything obviously wrong
>  with that; and it could well be no more guilty than shifting around
>  the kernel address space somewhat.  I've rather given up on the
>  bisection angle; and indeed, since found that how the problem
>  manifests varies somewhat from one day's git to another,
>  from one config to another.
>
>  It does not happen with maxcpus=1.  Yesterday it occurred to me
>  to try without CONFIG_PREEMPT=y; but reached no conclusion on that,
>  it turns out preemption has been somehow essential to resume from
>  RAM on this machine since before 2.6.25: clearly a separate issue.
>  And resume from RAM running 64-bit on it is also long problematic.
>
>  To reproduce the problem, I start off by building a kernel with
>  make -j3 (from habit, perhaps with priming the pagecache in mind),
>  then interrupt that around the time it gets to filemap.o, bootmem.o.
>  I pm-suspend, close the lid, wait a few seconds, open the lid;
>  make mrproper and start a make -j3 build again.  (Though the very
>  first time I noticed the problem, it was a segfault in a git pull
>  after resume.)
>
>  How quickly it goes bad varies a lot: often hangs right at the
>  start while sedding stuff before getting down to the build itself.
>  Often gets well into the build before gcc reports Real-time signal
>  (most commonly 14 but others seen) killed cc1.  But my favourite,
>  the most distinctive failure, is segfault (usually in sh or make)
>  at 20295564 ip .....2f2 error 6 in ld-2.6.1.so (openSUSE 10.3).
>
>  Always 20295564; and objdumping ld-2.6.1.so shows 0x14 of that is
>  just the offset from %edi, so the crucial address is 0x20295550.
>  Which is "PU) ", though I've not found that string anywhere in
>  the running vmlinux (but of course it does appear in kernel source).
>
>  Yesterday morning's git looked promising: because of the libata
>  70sec delay, I got diverted after the resume from RAM, left that
>  laptop idle, and found hald-something-or-other had come in every
>  few minutes and got that segfault at 20295564 (but with increasing
>  ip addresses: some address-space randomization effect, I suppose).
>  Well, I suppose it probably got run more often, but I'd only notice
>  the segfaulting ones.  So it can happen when close to idle; but
>  I've not been able to reproduce that since.
>
>  It's such a good signature, but I've failed to make progress with it.
>  Ted, please try doing the same (and check your logs for existing
>  segfault messages): let's see if you get the same number ;)
>  though I've no idea what it'd tell us.
>
>  Hugh
>

I can't reproduce it neither, and looking at the code over and over
again, see no obvious point for the breakage. I'll try to reproduce it
myself,
to see if I can spot something. But correct me if I'm wrong, this is
all 64-bit machines, right?

I'm stuck with mostly 32-bit hardware, but will give it a try anyway.

-- 
Glauber Costa.
"Free as in Freedom"
http://glommer.net

"The less confident you are, the more serious you have to act."
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