x86: prevent dereferencing non-allocated per_cpu variables

'for_each_possible_cpu(i)' when there's a _remote possibility_ of
dereferencing a non-allocated per_cpu variable involved.

All files except mm/vmstat.c are x86 arch.

Thanks to pageexec@freemail.hu for pointing this out.
Signed-off-by: NMike Travis <travis@sgi.com>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: <pageexec@freemail.hu>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/smp_32.c

@@ -223,7 +223,7 @@ void send_IPI_mask_sequence(cpumask_t mask, int vector)
 	 */ 
 
 	local_irq_save(flags);
-	for (query_cpu = 0; query_cpu < NR_CPUS; ++query_cpu) {
+	for_each_possible_cpu(query_cpu) {
 		if (cpu_isset(query_cpu, mask)) {
 			__send_IPI_dest_field(cpu_to_logical_apicid(query_cpu),
 					      vector);
@@ -675,7 +675,7 @@ static int convert_apicid_to_cpu(int apic_id)
 {
 	int i;
 
-	for (i = 0; i < NR_CPUS; i++) {
+	for_each_possible_cpu(i) {
 		if (per_cpu(x86_cpu_to_apicid, i) == apic_id)
 			return i;
 	}

arch/x86/kernel/smpboot_32.c

@@ -1090,7 +1090,7 @@ static void __init smp_boot_cpus(unsigned int max_cpus)
 	 * Allow the user to impress friends.
 	 */
 	Dprintk("Before bogomips.\n");
-	for (cpu = 0; cpu < NR_CPUS; cpu++)
+	for_each_possible_cpu(cpu)
 		if (cpu_isset(cpu, cpu_callout_map))
 			bogosum += cpu_data(cpu).loops_per_jiffy;
 	printk(KERN_INFO
@@ -1121,7 +1121,7 @@ static void __init smp_boot_cpus(unsigned int max_cpus)
 	 * construct cpu_sibling_map, so that we can tell sibling CPUs
 	 * efficiently.
 	 */
-	for (cpu = 0; cpu < NR_CPUS; cpu++) {
+	for_each_possible_cpu(cpu) {
 		cpus_clear(per_cpu(cpu_sibling_map, cpu));
 		cpus_clear(per_cpu(cpu_core_map, cpu));
 	}

arch/x86/xen/smp.c

@@ -146,7 +146,7 @@ void __init xen_smp_prepare_boot_cpu(void)
 	   old memory can be recycled */
 	make_lowmem_page_readwrite(&per_cpu__gdt_page);
 
-	for (cpu = 0; cpu < NR_CPUS; cpu++) {
+	for_each_possible_cpu(cpu) {
 		cpus_clear(per_cpu(cpu_sibling_map, cpu));
 		/*
 		 * cpu_core_map lives in a per cpu area that is cleared
@@ -163,7 +163,7 @@ void __init xen_smp_prepare_cpus(unsigned int max_cpus)
 {
 	unsigned cpu;
 
-	for (cpu = 0; cpu < NR_CPUS; cpu++) {
+	for_each_possible_cpu(cpu) {
 		cpus_clear(per_cpu(cpu_sibling_map, cpu));
 		/*
 		 * cpu_core_ map will be zeroed when the per