Message-ID: <20091004174113.GB24418@elte.hu>
Date:	Sun, 4 Oct 2009 19:41:13 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jason Baron <jbaron@...hat.com>
Cc:	Justin Mattock <justinmattock@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Li Zefan <lizf@...fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: system gets stuck in a lock during boot


* Jason Baron <jbaron@...hat.com> wrote:

> On Mon, Sep 07, 2009 at 02:49:44PM -0700, Justin Mattock wrote:
> > >>
> > >> * Justin P. Mattock<justinmattock@...il.com>  wrote:
> > >>
> > >>
> > >>>
> > >>> Ingo Molnar wrote:
> > >>>
> > >>>>
> > >>>> * Justin Mattock<justinmattock@...il.com>   wrote:
> > >>>>
> > >>>>
> > >>>>
> > >>>>>
> > >>>>> O.K. I feel better, deleted
> > >>>>> my system, and threw in a minimal built system
> > >>>>> with only the bare essentials to boot.
> > >>>>> (just to make sure things are correct).
> > >>>>>
> > >>>>> unfortunately after building rc6 I'm still hitting
> > >>>>> this. really am not sure why this is happening.
> > >>>>>
> > >>>>>
> > >>>>
> > >>>> Could you please double-check the bisection result by doing this:
> > >>>>
> > >>>>   git revert af6af30c0f
> > >>>>
> > >>>> on the latest kernel and seeing whether that fixes the lockup?
> > >>>>
> > >>>> Bisections are very efficient and hence very sensitive as well to
> > >>>> minimal errors. Just one small mistake near the end of a bisection
> > >>>> can blame the wrong commit.
> > >>>>
> > >>>> So the best way to double-check such 100%-triggerable crashes is to
> > >>>> do the revert. I tried the revert and it can be done fine here.
> > >>>>
> > >>>> [ _If_ that does not fix the bug then to save time you can
> > >>>>     'backtrack' the bisection, instead of re-doing it completely.
> > >>>>     I.e. you have your bisection log, re-check the final steps going
> > >>>>     backwards. Once you find a discrepancy (i.e. a 'bad' point that
> > >>>>     is 'good' or the other way around), redo the bisection log
> > >>>>     commands up to that point and continue it up to the end. ]
> > >>>>
> > >>>>        Ingo
> > >>>>
> > >>>>
> > >>>>
> > >>>
> > >>> shoot, I did not see your post here. when looking at my bisect
> > >>> log, I guess after a git bisect reset it clears?
> > >>>
> > >>> Anyways after git bisect had finished I looked manually at the
> > >>> commits that it had generated the one which I had sent in a post
> > >>> previously, and this one:
> > >>>
> > >>>  9424edc2da097c8589fcc24a72552d33e54be161
> > >>>
> > >>
> > >> (this commit has no effect on your kernel image, at all.)
> > >>
> > >>
> > >
> > > yep. but it was worth a try.
> > >>>
> > >>> at the time looking at the commit, I see this to be more of the
> > >>> cause because of it being related to elf as so forth, but as soon
> > >>> as I reverted this on rc6 made no difference.(the previous commit
> > >>> fixes this for me, on a regular tar.ball as well as in git.
> > >>>
> > >>> I think at this point since this system is a fresh from scratch
> > >>> build, I think something might be wrong that I'm doing (all the
> > >>> CFLAGS, and such are in a previous post).
> > >>>
> > >>> At the moment I don't have a problem applying a patch to the
> > >>> kernel for this. especially since I'm the only one that seems to
> > >>> be hitting this, then if more and more reports of this happen then
> > >>> we can go from there.
> > >>>
> > >>
> > >> What would be nice is to verify your bisection end result, i.e. do
> > >> what i suggested:
> > >>
> > >>
> > >
> > > yeah I've done this on both kernels three to be exact, and all boot after
> > > reverting
> > > Fix perf-tracepoint OOPS.
> > >
> > > As for my system, I'm still convinced that I might be doing something wrong
> > > over here.
> > >
> > >>>> Could you please double-check the bisection result by doing this:
> > >>>>
> > >>>>   git revert af6af30c0f
> > >>>>
> > >>>> on the latest kernel and seeing whether that fixes the lockup?
> > >>>>
> > >>
> > >> if this doesnt fix it on latest -git then this commit is not the
> > >> cause of the lockup.
> > >>
> > >>        Ingo
> > >>
> > >>
> > >
> > > This commit(Fix perf-tracepoint OOPS.)does fix my stuckage, but I'm left, as
> > > well as others asking
> > > the question of why.
> > > In any case I still think I'm setting something wrong with either gcc, or
> > > something
> > > that might be causing this from userland.
> > >
> > > Justin P. Mattock
> > >
> > 
> > O.k. here something awkward about this issue I was
> > experiencing. at the moment I have two imac's
> > here the descriptions:
> > 
> > imac A) the one with the problem
> > 
> > OS: built from the clfs book
> > x86_64 multilib with only lib64
> > 
> > built everything with these flags:
> > CFLAGS="-m64 -mtune=core2 -march=core2
> > -mfpmath=both -O2 -pipe -fomit-frame-pointer
> > -fstack-protection"
> > CXXFLAGS="${CFLAGS}" MAKEOPTS="{-j3}"
> > while compiling everything with
> > gcc version: 4.5.0 20090730
> > 
> > 
> > imac B) the one that works
> > 
> > OS: clfs(just built a few days ago)
> > x86_64 pure64 bit build
> > (lib with a symlink to lib64)
> > CFLAGS="-m64 -mtune=core2 -march=core2
> >  -O2 -pipe -fomit-frame-pointer"
> > CXXFLAGS="${CFLAGS}" MAKEOPTS="{-j3}"
> > gcc version: 4.4.1 (GCC for Cross-LFS 4.4.1.20090722)
> > 
> > The only things I can think of is either I hit something
> > because of gcc, something goes wrong with the libraries,
> > or there something happening with either the option
> > of mfpmath=both or stackprotection.
> > 
> > At this point since the kernel seems to be running fine,
> > is to just trash the system that has this issue and just leave
> > it at, I was hitting some weird anomaly.
> > 
> 
> hi Justin,
> 
> I've been playing around with gcc '4.5' as well and hit a panic that
> looks very similar to what you've seen with stock 2.6.31 - I haven't
> seen it anywhere else. Anyways, it seems to be some sort of alignment
> issue with the 'struct ftrace_event_call'. I'm not sure yet if this is a
> compiler or kernel issue. But the following kernel patch fixes the issue
> for me. It would be interesting to verify if the patch also resolves the
> issue for you.

Would be nice to know precisely what kind of problem is being hit here - 
we'd like to fix either the kernel or GCC - depending on where the bug 
lies.

	Ingo
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