linux-kernel - Re: [Bug #14270] Cannot boot on a PIII Celeron

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Message-ID: <4AC891B4.20407@msgid.tls.msk.ru>
Date:	Sun, 04 Oct 2009 16:14:44 +0400
From:	Michael Tokarev <mjt@....msk.ru>
To:	Cyrill Gorcunov <gorcunov@...il.com>
CC:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>
Subject: Re: [Bug #14270] Cannot boot on a PIII Celeron

Michael Tokarev wrote:
> Cyrill Gorcunov wrote:
>> On 10/2/09, Michael Tokarev <mjt@....msk.ru> wrote:
>>> Michael Tokarev wrote:
>>>> Cyrill Gorcunov wrote:
>>>>> On 10/1/09, Rafael J. Wysocki <rjw@...k.pl> wrote:
>>>>>> This message has been generated automatically as a part of a report
>>>>>> of regressions introduced between 2.6.30 and 2.6.31.
>>>>>>
>>>>>> The following bug entry is on the current list of known regressions
>>>>>> introduced between 2.6.30 and 2.6.31.  Please verify if it still 
>>>>>> should
>>>>>> be listed and let me know (either way).
>>>>> Michael has been asked to bisect it (if possible). I cant reproduce it
>>>>> in kvm unfortunately.
>>>> Yes, and that's what I'll be trying to do shortly.
>>>> I had other issues to sort out and wasn't able to
>>>> get to it in few last days.
>>>>
>>>> Also I've a few other suspects.  For example, in this .31
>>>> config I changed from bzip to lzma compression - and that's
>>>> where (or near) kernel is rebooting.
>>> And that was the problem.  After switching from LZMA
>>> to BZIP2 kernel boots again.
>>>
>>> Dunno if it can be treated as a regression, but it's
>>> definitely a bug.
>>
>> thanks for tracking it down Michael!
>> Rafael, who is responsible for LZMA now?
>> Cc him please.
> 
> Please hold on for a while.
> 
> I switched to BZIP2, it booted fine.  I switched back to LZMA -
> and that one now boots too.  Original bzImage, which were built
> by the same compiler from the same source using the same
> options reboots.
> 
> So um... I'm now trying to reproduce it ;)

I performed about 20 kernel recompiles, and finally have some "statistics".
The problem is almost reproduceable, in a sense that I was able to get 6
more cases behaving the same way (rebooting right at early boot on a cel).
And all 3 "non-working" cases were with ccache.  Ie, about half out of ~25
compiles done with ccache, and 7 of the resulting kernels are buggy.  No
single failure without ccache so far.

Maybe it's some stale .o file cached by ccache (and it indeed looks like
that) -- I didn't try to remove the cache yet (but my guess is that I
wont be able to reproduce the issue with clean cache anymore).

What puzzles me most is the "failure mode".  The difference between the
two processors is minimal.  Having a corrupt .o file and almost-working
kernel is almost impossible by its own.  And hitting this difference with
a corrupt .o file is.. unbelievable.

So I'm declaring it's a false alarm for now, and closing the bug.

/mjt
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