Cc: linux-kernel@vger.kernel.org
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Date: Fri, 01 Feb 2008 22:06:56 +0100
From: "Gerhard Pircher" <gerhard_pircher@gmx.net>
In-Reply-To: <20080201202518.GJ18688@csn.ul.ie>
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 <20080201200518.174050@gmx.net> <20080201202518.GJ18688@csn.ul.ie>
Subject: Re: Commit for mm/page_alloc.c breaks boot process on my machine
To: Mel Gorman <mel@csn.ul.ie>
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-------- Original-Nachricht --------
> Datum: Fri, 1 Feb 2008 20:25:18 +0000
> Von: Mel Gorman <mel@csn.ul.ie>
> An: Gerhard Pircher <gerhard_pircher@gmx.net>
> CC: linux-kernel@vger.kernel.org
> Betreff: Re: Commit for mm/page_alloc.c breaks boot process on my machine

> I meant uninitialised memory but I also wonder could something like this
> happen if you are trying to use memory that doesn't exist. i.e. you are
> trying to access more memory than you really have but you indicate later
> that this is not the case.
Good question. The memory is in the physical address range from 0x00000000
to 0x60000000 (1536MB).

> > > 2. Any chance of seeing a dmesg log?
> > That's a little bit of a problem. The kernel log in memory doesn't show
> > any kernel oops, but is also fragmented (small fragments seem to have
> > been overwritten with 0x0).
> 
> err, that doesn't sound very healthy.
Yeah, I know. But the platform code hasn't changed much when porting it
from arch/ppc to arch/powerpc. That's why I'm a little bit lost in this
case. :-)

> > Well, I can't answer this question. The kernel currently locks up when
> > loading the INIT program. But that is another problem (I still have to
> > bisect it) and doesn't seem to be related to this problem.
> 
> INIT would be the first MOVABLE allocation so it would be using memory
> at the end of the physical adddress range. i.e. the crash happens when
> memory towards the end and the only difference between the patch applied
> and reverted is when it happens.
Oh, that sounds interesting!

> Could you try booting with 16MB less memory using mem=?
I started the kernel with 512MB RAM (mem=496) and 1.5GB (mem=1520). The
kernel oopes in both cases with a "Unable to handle kernel paging request
for data address 0xbffff000", followed by a "Oops: kernel access of bad
area, sig 11" message. The end of the stack trace shows the start_here()
function.
I'm not a PowerPC expert, but if 0xbffff000 is a virtual address, then
it would be in the user program address space, right? If it is a physical
address, then it is somewhere in the unallocated PCI address space.

Gerhard

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