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    Subject[PATCH v2 34/52] scsi, bnx2fc: 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_notifier_register_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_notifier_register_done();


    Fix the bnx2fc code in scsi by using this latter form of callback
    registration.

    Cc: Eddie Wai <eddie.wai@broadcom.com>
    Cc: "James E.J. Bottomley" <JBottomley@parallels.com>
    Cc: Ingo Molnar <mingo@kernel.org>
    Cc: linux-scsi@vger.kernel.org
    Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
    ---

    drivers/scsi/bnx2fc/bnx2fc_fcoe.c | 12 ++++++++++--
    1 file changed, 10 insertions(+), 2 deletions(-)

    diff --git a/drivers/scsi/bnx2fc/bnx2fc_fcoe.c b/drivers/scsi/bnx2fc/bnx2fc_fcoe.c
    index 9b94850..c4ec235 100644
    --- a/drivers/scsi/bnx2fc/bnx2fc_fcoe.c
    +++ b/drivers/scsi/bnx2fc/bnx2fc_fcoe.c
    @@ -2586,12 +2586,16 @@ static int __init bnx2fc_mod_init(void)
    spin_lock_init(&p->fp_work_lock);
    }

    + cpu_notifier_register_begin();
    +
    for_each_online_cpu(cpu) {
    bnx2fc_percpu_thread_create(cpu);
    }

    /* Initialize per CPU interrupt thread */
    - register_hotcpu_notifier(&bnx2fc_cpu_notifier);
    + __register_hotcpu_notifier(&bnx2fc_cpu_notifier);
    +
    + cpu_notifier_register_done();

    cnic_register_driver(CNIC_ULP_FCOE, &bnx2fc_cnic_cb);

    @@ -2656,13 +2660,17 @@ static void __exit bnx2fc_mod_exit(void)
    if (l2_thread)
    kthread_stop(l2_thread);

    - unregister_hotcpu_notifier(&bnx2fc_cpu_notifier);
    + cpu_notifier_register_begin();

    /* Destroy per cpu threads */
    for_each_online_cpu(cpu) {
    bnx2fc_percpu_thread_destroy(cpu);
    }

    + __unregister_hotcpu_notifier(&bnx2fc_cpu_notifier);
    +
    + cpu_notifier_register_done();
    +
    destroy_workqueue(bnx2fc_wq);
    /*
    * detach from scsi transport


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