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    Subject[PATCH] x86: Fix NULL pointer dereference on CPU hotplug after disabling irqs
    In current Linux, percpu variable `vector_irq' is not cleared on offlined
    cpus while disabling devices' irqs. If the cpu that has the disabled irqs
    in vector_irq is hotplugged, __setup_vector_irq() hits invalid irq vector
    and may crash.

    This bug can be reproduced as following;
    # echo 0 > /sys/devices/system/cpu/cpu7/online
    # modprobe -r some_driver_using_interrupts # vector_irq@cpu7 uncleared
    # echo 1 > /sys/devices/system/cpu/cpu7/online # kernel may crash

    This patch fixes this bug by clearing vector_irq in __clear_irq_vector()
    even if the cpu is offlined.

    Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: x86@kernel.org
    Cc: linux-kernel@vger.kernel.org
    ---
    arch/x86/kernel/apic/io_apic.c | 4 ++--
    1 files changed, 2 insertions(+), 2 deletions(-)

    diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
    index ac96561..5f0ff59 100644
    --- a/arch/x86/kernel/apic/io_apic.c
    +++ b/arch/x86/kernel/apic/io_apic.c
    @@ -1195,7 +1195,7 @@ static void __clear_irq_vector(int irq, struct irq_cfg *cfg)
    BUG_ON(!cfg->vector);
    vector = cfg->vector;
    - for_each_cpu_and(cpu, cfg->domain, cpu_online_mask)
    + for_each_cpu(cpu, cfg->domain)
    per_cpu(vector_irq, cpu)[vector] = -1;
    cfg->vector = 0;
    @@ -1203,7 +1203,7 @@ static void __clear_irq_vector(int irq, struct irq_cfg *cfg)
    if (likely(!cfg->move_in_progress))
    return;
    - for_each_cpu_and(cpu, cfg->old_domain, cpu_online_mask) {
    + for_each_cpu(cpu, cfg->old_domain) {
    for (vector = FIRST_EXTERNAL_VECTOR; vector < NR_VECTORS;
    vector++) {
    if (per_cpu(vector_irq, cpu)[vector] != irq)
    --
    1.7.7.6


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