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    Subject[PATCH 21/51] x86, intel, cacheinfo: Fix CPU hotplug callback registration
    Date
    Subsystems that want to register CPU hotplug callbacks, as well as perform
    initialization for the CPUs that are already online, often do it as shown
    below:

    get_online_cpus();

    for_each_online_cpu(cpu)
    init_cpu(cpu);

    register_cpu_notifier(&foobar_cpu_notifier);

    put_online_cpus();

    This is wrong, since it is prone to ABBA deadlocks involving the
    cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
    with CPU hotplug operations).

    Instead, the correct and race-free way of performing the callback
    registration is:

    cpu_maps_update_begin();

    for_each_online_cpu(cpu)
    init_cpu(cpu);

    /* Note the use of the double underscored version of the API */
    __register_cpu_notifier(&foobar_cpu_notifier);

    cpu_maps_update_done();


    Fix the intel cacheinfo code in x86 by using this latter form of callback
    registration.

    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: x86@kernel.org
    Cc: Borislav Petkov <bp@suse.de>
    Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
    ---

    arch/x86/kernel/cpu/intel_cacheinfo.c | 13 ++++++++-----
    1 file changed, 8 insertions(+), 5 deletions(-)

    diff --git a/arch/x86/kernel/cpu/intel_cacheinfo.c b/arch/x86/kernel/cpu/intel_cacheinfo.c
    index 0641113..d15c0dc 100644
    --- a/arch/x86/kernel/cpu/intel_cacheinfo.c
    +++ b/arch/x86/kernel/cpu/intel_cacheinfo.c
    @@ -1225,21 +1225,24 @@ static struct notifier_block cacheinfo_cpu_notifier = {

    static int __init cache_sysfs_init(void)
    {
    - int i;
    + int i, err = 0;

    if (num_cache_leaves == 0)
    return 0;

    + cpu_maps_update_begin();
    for_each_online_cpu(i) {
    - int err;
    struct device *dev = get_cpu_device(i);

    err = cache_add_dev(dev);
    if (err)
    - return err;
    + goto out;
    }
    - register_hotcpu_notifier(&cacheinfo_cpu_notifier);
    - return 0;
    + __register_hotcpu_notifier(&cacheinfo_cpu_notifier);
    +
    +out:
    + cpu_maps_update_done();
    + return err;
    }

    device_initcall(cache_sysfs_init);


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