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    Subject[23/91] x86, hotplug: Serialize CPU hotplug to avoid bringup concurrency issues
    2.6.34-stable review patch.  If anyone has any objections, please let us know.

    ------------------

    From: Borislav Petkov <bp@amd64.org>

    commit d7c53c9e822a4fefa13a0cae76f3190bfd0d5c11 upstream.

    When testing cpu hotplug code on 32-bit we kept hitting the "CPU%d:
    Stuck ??" message due to multiple cores concurrently accessing the
    cpu_callin_mask, among others.

    Since these codepaths are not protected from concurrent access due to
    the fact that there's no sane reason for making an already complex
    code unnecessarily more complex - we hit the issue only when insanely
    switching cores off- and online - serialize hotplugging cores on the
    sysfs level and be done with it.

    [ v2.1: fix !HOTPLUG_CPU build ]

    Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
    LKML-Reference: <20100819181029.GC17171@aftab>
    Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
    index a84fc34..ac7827f 100644
    --- a/arch/x86/Kconfig
    +++ b/arch/x86/Kconfig
    @@ -245,6 +245,11 @@ config ARCH_HWEIGHT_CFLAGS

    config KTIME_SCALAR
    def_bool X86_32
    +
    +config ARCH_CPU_PROBE_RELEASE
    + def_bool y
    + depends on HOTPLUG_CPU
    +
    source "init/Kconfig"
    source "kernel/Kconfig.freezer"

    diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
    index abf4a86..8b3bfc4 100644
    --- a/arch/x86/kernel/smpboot.c
    +++ b/arch/x86/kernel/smpboot.c
    @@ -90,6 +90,25 @@ DEFINE_PER_CPU(int, cpu_state) = { 0 };
    static DEFINE_PER_CPU(struct task_struct *, idle_thread_array);
    #define get_idle_for_cpu(x) (per_cpu(idle_thread_array, x))
    #define set_idle_for_cpu(x, p) (per_cpu(idle_thread_array, x) = (p))
    +
    +/*
    + * We need this for trampoline_base protection from concurrent accesses when
    + * off- and onlining cores wildly.
    + */
    +static DEFINE_MUTEX(x86_cpu_hotplug_driver_mutex);
    +
    +void cpu_hotplug_driver_lock()
    +{
    + mutex_lock(&x86_cpu_hotplug_driver_mutex);
    +}
    +
    +void cpu_hotplug_driver_unlock()
    +{
    + mutex_unlock(&x86_cpu_hotplug_driver_mutex);
    +}
    +
    +ssize_t arch_cpu_probe(const char *buf, size_t count) { return -1; }
    +ssize_t arch_cpu_release(const char *buf, size_t count) { return -1; }
    #else
    static struct task_struct *idle_thread_array[NR_CPUS] __cpuinitdata ;
    #define get_idle_for_cpu(x) (idle_thread_array[(x)])



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