[PATCH 32/51] scsi, bnx2fc: Fix CPU hotplug callback registration

[Srivatsa S. Bhat]

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

Cc: Eddie Wai <eddie....@broadcom.com>
Cc: "James E.J. Bottomley" <jbottom...@parallels.com>
Cc: linux-scsi@vger.kernel.org
Signed-off-by: Srivatsa S. Bhat <srivatsa.b...@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..f6c10c5 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_maps_update_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_maps_update_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_maps_update_begin();
 
        /* Destroy per cpu threads */
        for_each_online_cpu(cpu) {
                bnx2fc_percpu_thread_destroy(cpu);
        }
 
+       __unregister_hotcpu_notifier(&bnx2fc_cpu_notifier);
+
+       cpu_maps_update_done();
+
        destroy_workqueue(bnx2fc_wq);
        /*
         * detach from scsi transport

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