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Re: Kernel crash in 2.6.32.6 / bcm1480 with 16k page size

To: Ralf Baechle <ralf@linux-mips.org>
Subject: Re: Kernel crash in 2.6.32.6 / bcm1480 with 16k page size
From: Guenter Roeck <guenter.roeck@ericsson.com>
Date: Fri, 29 Jan 2010 07:12:20 -0800
Cc: "linux-mips@linux-mips.org" <linux-mips@linux-mips.org>
In-reply-to: <20100129132406.GD5685@linux-mips.org>
References: <20100128155514.GA31611@ericsson.com> <20100129132406.GD5685@linux-mips.org>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mutt/1.5.18 (2008-05-17)
On Fri, Jan 29, 2010 at 08:24:07AM -0500, Ralf Baechle wrote:
> On Thu, Jan 28, 2010 at 07:55:14AM -0800, Guenter Roeck wrote:
> > 
> > I get the following kernel crash when running a 2.6.32.6 kernel on a 
> > bcm1480 cpu.
> > It only happens if I configure a page size of 16k or 64k; 4k page size is 
> > fine.
> > 
> > A similar problem was recently fixed for ppc. It turned out to be a problem 
> > in ppc
> > specific memory management code, so that fix won't help here.
> > 
> > Has anyone else seen this before ? Any idea where to start looking for the 
> > problem ?
> 
> Supposedly this was working for SB1.  I suggest you find an older kernel
> version that works for your with 16k pages then use git bisect to find
> the problem.
> 
It used to work with 2.6.27.

However, bisect won't work, because the code in question (per cpu memory 
allocation) was
completely rewritten since then.

The new percpu code tries to allocate memory just below VMALLOC_END. This works 
on sb1 for
a page size of 4k, but not for a page size of 16k and 64k. The value of 
VMALLOC_END depends
on the page size.

ppc had a similar problem. It had nothing to do with the new percpu memory 
allocation code,
but with memory alocation close to VMALLOC_END. In other words, it was a 
day-one bug which
was never noticed because allocating memory in that address space is highly 
unlikely.

I suspect the same is the case here. I could write some code for 2.6.27, to 
test the same
memory allocation there, but I am quite sure the problem is going to show up 
there as well.

So first question would be: Has anyone successfully loaded a 64 bit mips kernel 
with 2.6.32 
and a page size of 16k or 64k ? This would at least help me reducing the 
problem to sb1.

Thanks,
Guenter

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