linux-kernel - Re: 2.6.28-rc9 panics with crashkernel=256M while booting

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Date:	Wed, 7 Jan 2009 18:28:13 +0530
From:	Chandru <chandru@...ibm.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	Paul Mackerras <paulus@...ba.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: 2.6.28-rc9 panics with crashkernel=256M while booting

On Monday 05 January 2009 22:00:33 Dave Hansen wrote:
> OK, I had to think about this for a good, long time.  That's bad. :)
>
> There are two things that we're dealing with here: "active regions" and
> the NODE_DATA's.  The if() you've pasted above resizes the reservation
> so that it fits into the current active region.  However, as you noted,
> we haven't resized it so that it fits into the NODE_DATA() that we're
> looking at.  We call into the bootmem code, and BUG_ON().
>
> The thing I don't like about this is that it might hide bugs in other
> callers.  This really is a ppc-specific thing and, although what you
> wrote will fix the bug on ppc, it will probably cause someone in the
> future to call reserve_bootmem_node() with too large a reservation and
> get a silent failure (not reserving the requested size) back.
>
> We really do need to go take a hard look at the whole interaction
> between lmb's, node active regions, and the NUMA code some day.  It has
> kinda grown to be a bit ungainly.
>
> How about we just consult the NODE_DATA() in
> mark_reserved_regions_for_nid() instead of reserve_bootmem_node()?

I don't know how you wanted NODE_DATA() to be consulted here. i.e before 
calling reserve_bootmem_node() should we have a condition 

	if (PFN_UP(physbase+reserve_size) > node_end_pfn) 
	then
		resize reserve_size again so that PFN_UP() will equate to node_end_pfn ??
	end 

Also I was wondering if in reserve_bootmem_node()
	end = PFN_DOWN() ; will do.. 

With the recent changes from you that went into 2.6.28 stable 
(commit:a4c74ddd5ea3db53fc73d29c222b22656a7d05be), it worked on the system 
with PFN_DOWN(). 

Thanks,
Chandru
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