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

Mel Gorman
2009-09-21T17:42:20Z

On Mon, Sep 21, 2009 at 10:17:52AM -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@csn.ul.ie>
> > ---
> > 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.)

D'oh, will clean it up in the next revision if the substance of the
patch is agreed upon.

> You also spelled initializing wrong.

It's spelt correctly for British English.

--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab