Re: [PATCH 1/3] powerpc: Allocate per-cpu areas for node IDs forSLQB to use as per-node areas

[Randy Dunlap]

On Mon, 21 Sep 2009 10:17:52 -0700 Daniel Walker wrote:

> On Mon, 2009-09-21 at 17:10 +0100, Mel Gorman wrote:
> > SLQB uses DEFINE_PER_CPU to define per-node areas. An implicit
> > assumption is made that all valid node IDs will have matching valid CPU
> > ids. In memoryless configurations, it is possible to have a node ID with
> > no CPU having the same ID. When this happens, a per-cpu are is not
> > created and the value of paca[cpu].data_offset is some random value.
> > This is later deferenced and the system crashes after accessing some
> > invalid address.
> > 
> > This patch hacks powerpc to allocate per-cpu areas for node IDs that
> > have no corresponding CPU id. This gets around the immediate problem but
> > it should be discussed if there is a requirement for a DEFINE_PER_NODE
> > and how it should be implemented.
> > 
> > Signed-off-by: Mel Gorman <mel@xxxxxxxxx>
> > ---
> >  arch/powerpc/kernel/setup_64.c |   20 ++++++++++++++++++++
> >  1 files changed, 20 insertions(+), 0 deletions(-)
> > 
> > diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
> > index 1f68160..a5f52d4 100644
> > --- a/arch/powerpc/kernel/setup_64.c
> > +++ b/arch/powerpc/kernel/setup_64.c
> > @@ -588,6 +588,26 @@ void __init setup_per_cpu_areas(void)
> >  		paca[i].data_offset = ptr - __per_cpu_start;
> >  		memcpy(ptr, __per_cpu_start, __per_cpu_end - __per_cpu_start);
> >  	}
> > +#ifdef CONFIG_SLQB
> > +	/* 
> > +	 * SLQB abuses DEFINE_PER_CPU to setup a per-node area. This trick
> > +	 * assumes that ever node ID will have a CPU of that ID to match.
> > +	 * On systems with memoryless nodes, this may not hold true. Hence,
> > +	 * we take a second pass initialising a "per-cpu" area for node-ids
> > +	 * that SLQB can use
> > +	 */
> 
> Very trivial, but there's a little trailing whitespace in the first line
> of the comment (checkpatch warns on it.) You also spelled initializing
> wrong.

re: spelling.  Not really.  Think internationally.

---
~Randy
LPC 2009, Sept. 23-25, Portland, Oregon
http://linuxplumbersconf.org/2009/
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