From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id 50EEC6B0062 for ; Mon, 21 Sep 2009 13:17:46 -0400 (EDT) Sender: owner-linux-mm@kvack.org Subject: Re: [PATCH 1/3] powerpc: Allocate per-cpu areas for node IDs for SLQB to use as per-node areas From: Daniel Walker In-Reply-To: <1253549426-917-2-git-send-email-mel@csn.ul.ie> References: <1253549426-917-1-git-send-email-mel@csn.ul.ie> <1253549426-917-2-git-send-email-mel@csn.ul.ie> Content-Type: text/plain Date: Mon, 21 Sep 2009 10:17:52 -0700 Message-Id: <1253553472.9654.236.camel@desktop> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit To: Mel Gorman Cc: Nick Piggin , Pekka Enberg , Christoph Lameter , heiko.carstens@de.ibm.com, sachinp@in.ibm.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Tejun Heo , Benjamin Herrenschmidt List-ID: 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 > --- > 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. Daniel -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org