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    Subject[PATCH 1/1] mm: Prevent dereferencing non-allocated per_cpu variables
    Change loops controlled by 'for (i = 0; i < NR_CPUS; i++)' to use
    '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.

    Based on 2.6.24-rc3-mm1 .

    Thanks to pageexec@freemail.hu for pointing this out.

    Signed-off-by: Mike Travis <travis@sgi.com>
    ---
    arch/x86/kernel/smp_32.c | 4 ++--
    arch/x86/kernel/smpboot_32.c | 4 ++--
    arch/x86/xen/smp.c | 4 ++--
    mm/vmstat.c | 4 ++--
    4 files changed, 8 insertions(+), 8 deletions(-)

    --- a/arch/x86/kernel/smp_32.c
    +++ b/arch/x86/kernel/smp_32.c
    @@ -223,7 +223,7 @@ void send_IPI_mask_sequence(cpumask_t ma
    */

    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 api
    {
    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;
    }
    --- a/arch/x86/kernel/smpboot_32.c
    +++ b/arch/x86/kernel/smpboot_32.c
    @@ -1091,7 +1091,7 @@ static void __init smp_boot_cpus(unsigne
    * 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
    @@ -1122,7 +1122,7 @@ static void __init smp_boot_cpus(unsigne
    * 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));
    }
    --- a/arch/x86/xen/smp.c
    +++ b/arch/x86/xen/smp.c
    @@ -146,7 +146,7 @@ void __init xen_smp_prepare_boot_cpu(voi
    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(unsigne
    {
    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
    --- a/mm/vmstat.c
    +++ b/mm/vmstat.c
    @@ -27,12 +27,12 @@ static void sum_vm_events(unsigned long
    memset(ret, 0, NR_VM_EVENT_ITEMS * sizeof(unsigned long));

    cpu = first_cpu(*cpumask);
    - while (cpu < NR_CPUS) {
    + while (cpu < NR_CPUS && cpu_possible(cpu)) {
    struct vm_event_state *this = &per_cpu(vm_event_states, cpu);

    cpu = next_cpu(cpu, *cpumask);

    - if (cpu < NR_CPUS)
    + if (cpu < NR_CPUS && cpu_possible(cpu))
    prefetch(&per_cpu(vm_event_states, cpu));


    --

    -
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