linux-kernel - [PATCH] Inhibit machine from asserting an NMI when doing Alt-SysRq-M operation.

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Message-ID: <20070327134508.GA21548@andromeda.dapyr.net>
Date:	Tue, 27 Mar 2007 09:45:08 -0400
From:	Konrad Rzeszutek <konrad@...nok.org>
To:	linux-kernel@...r.kernel.org
Cc:	konradr@...hat.com, konradr@...ibm.com
Subject: [PATCH] Inhibit machine from asserting an NMI when doing Alt-SysRq-M operation.

This patch touches the NMI watchdog every MAX_ORDER_NR_PAGES
to inhibit the machine from triggering an NMI while the CPUs
are locked. This situation is happening on boxes with more 
than 64CPUs and 128GB of RAM when Alt-SysRq-m is performed.

It has been succesfully tested for regression on uni, 2, 4, 8 
32, and 64 CPU boxes with various memory configuration.

diff --git a/arch/x86_64/mm/init.c b/arch/x86_64/mm/init.c
index ec31534..fd7f8a6 100644
--- a/arch/x86_64/mm/init.c
+++ b/arch/x86_64/mm/init.c
@@ -26,6 +26,7 @@ #include <linux/poison.h>
 #include <linux/dma-mapping.h>
 #include <linux/module.h>
 #include <linux/memory_hotplug.h>
+#include <linux/nmi.h>

 #include <asm/processor.h>
 #include <asm/system.h>
@@ -72,6 +73,11 @@ void show_mem(void)

 	for_each_online_pgdat(pgdat) {
                for (i = 0; i < pgdat->node_spanned_pages; ++i) {
+			/* this loop can take a while with 256 GB and 4k pages
+			   so update the NMI watchdog */
+			if (unlikely(i % MAX_ORDER_NR_PAGES == 0)) {
+				touch_nmi_watchdog();
+			}
 			page = pfn_to_page(pgdat->node_start_pfn + i);
 			total++;
 			if (PageReserved(page))
-
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