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

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Date:	Mon, 21 Sep 2009 17:10:24 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Nick Piggin <npiggin@...e.de>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Christoph Lameter <cl@...ux-foundation.org>
Cc:	heiko.carstens@...ibm.com, sachinp@...ibm.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Mel Gorman <mel@....ul.ie>, Tejun Heo <tj@...nel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: [PATCH 1/3] powerpc: Allocate per-cpu areas for node IDs for SLQB to use as per-node areas

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@....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
+	 */
+	for_each_node_state(i, N_NORMAL_MEMORY) {
+
+		/* Skip node IDs that a valid CPU id exists for */
+		if (paca[i].data_offset)
+			continue;
+
+		ptr = alloc_bootmem_pages_node(NODE_DATA(cpu_to_node(i)), size);
+
+		paca[i].data_offset = ptr - __per_cpu_start;
+		memcpy(ptr, __per_cpu_start, __per_cpu_end - __per_cpu_start);
+	}
+#endif /* CONFIG_SLQB */
 }
 #endif
 
-- 
1.6.3.3

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