linux-kernel - Re: frame unwinder patches

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Date:	Fri, 5 Sep 2008 15:52:47 +0200
From:	Bernd Schubert <bs@...eap.de>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>
Subject: Re: frame unwinder patches

On Friday 05 September 2008 15:33:17 Arjan van de Ven wrote:
> On Fri, 5 Sep 2008 11:19:21 +0200
>
> Bernd Schubert <bs@...eap.de> wrote:
> > > not printing the ? would be trivial (for some backtraces we do
> > > that), but so far hasn't been seen as desirable because you lose
> > > information in those hard-to-debug cases when you need anything you
> > > can get from the backtrace.
> >
> > I see your point, but in most cases it is rather annoying.
>
> ... if you see backtraces regularly there's something wrong ;-)

It always depends on what you are doing. Presently I'm fixing the 
reset-handler of the mpt fusion driver and since I'm not 
$hardcore_kernel_hacker_with_super_scsi_knowlegde, but only know C and a 
little bit about the kernel API I insert dump_stack() and printks all over 
the place into the code to understand what is going on.

Well, this reset part is mostly done, now this problem: 
http://marc.info/?l=linux-scsi&m=118039573814323&w=2

So yes, there is something wrong ;) Unfortunately so far nobody cared about 
these bugs we are hitting regularily.

>
> (and if you really care it's 1 line of code to turn it off)

It is not only this, I think the dwarf2 stack unwinder patches provide by far 
better traces than the in-kernel unwinder. At least ever since I applied 
these patches to our kernels, I was able to read the stack dumps...

Cheers,
Bernd

-- 
Bernd Schubert
Q-Leap Networks GmbH
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