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Subject: Re: 2.6.31-git5 kernel boot hangs on powerpc
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Tejun Heo <tj@kernel.org>
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Date: Fri, 25 Sep 2009 13:40:06 +1000
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Cc: Linux/PPC Development <linuxppc-dev@ozlabs.org>,
	David Miller <davem@davemloft.net>
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On Fri, 2009-09-25 at 12:22 +0900, Tejun Heo wrote:
> Benjamin Herrenschmidt wrote:
> >> --- Exception: 301 at .memset+0x60/0xfc
> >>     LR = .pcpu_alloc+0x718/0x8fc
> > 
> > So it's memsetting something that causes it to hash_page(), ie, faulting
> > in pages (vmalloc space ?) so far nothing obviously wrong....
> 
> It's probably memset() call near the end of pcpu_populate_chunk()
> where percpu allocator clears the allocated areas before returning to
> user.  I don't think the first chunk is causing the problem as they're
> all in the linear mapped area.  From the second chunk on, they're on
> vmalloc area and very near to the top of it, so that might be exposing
> a hidden problem in paging code?  BTW, for some reason, the problem is
> not reproducible on my powerstation.

That's indeed a possibility, though it would be strange...

Definitely worth looking at your logs, and I'll check with Sachin
about getting on the machine after that if I need to dig more.

Cheers,
Ben.