linux-kernel - Re: [PATCH 1/1] mm: Prevent dereferencing non-allocated per

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Date:	Tue, 27 Nov 2007 16:09:41 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	andi@...stfloor.org, travis@....com, ak@...e.de,
	pageexec@...email.hu, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] mm: Prevent dereferencing non-allocated per_cpu
 variables

On Tue, 27 Nov 2007, Andrew Morton wrote:

> I don't recall anyone ever demonstrating that prefetch is useful in-kernel.

vmstat: remove prefetch

Remove the prefetch logic in order to avoid touching impossible per cpu 
areas.

Signed-off-by: Christoph Lameter <clameter@....com>

---
 mm/vmstat.c |   11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

Index: linux-2.6/mm/vmstat.c
===================================================================
--- linux-2.6.orig/mm/vmstat.c	2007-11-27 16:04:15.345713812 -0800
+++ linux-2.6/mm/vmstat.c	2007-11-27 16:07:00.552713192 -0800
@@ -21,21 +21,14 @@ EXPORT_PER_CPU_SYMBOL(vm_event_states);
 
 static void sum_vm_events(unsigned long *ret, cpumask_t *cpumask)
 {
-	int cpu = 0;
+	int cpu;
 	int i;
 
 	memset(ret, 0, NR_VM_EVENT_ITEMS * sizeof(unsigned long));
 
-	cpu = first_cpu(*cpumask);
-	while (cpu < NR_CPUS) {
+	for_each_cpu_mask(cpu, *cpumask) {
 		struct vm_event_state *this = &per_cpu(vm_event_states, cpu);
 
-		cpu = next_cpu(cpu, *cpumask);
-
-		if (cpu < NR_CPUS)
-			prefetch(&per_cpu(vm_event_states, cpu));
-
-
 		for (i = 0; i < NR_VM_EVENT_ITEMS; i++)
 			ret[i] += this->event[i];
 	}
-
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