[PATCH 33/51] scsi, fcoe: 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 fcoe code in scsi by using this latter form of callback registration.

Cc: Robert Love <robert.w.l...@intel.com>
Cc: "James E.J. Bottomley" <jbottom...@parallels.com>
Cc: fcoe-de...@open-fcoe.org
Cc: linux-scsi@vger.kernel.org
Signed-off-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
---

 drivers/scsi/fcoe/fcoe.c |   15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/fcoe/fcoe.c b/drivers/scsi/fcoe/fcoe.c
index f317000..1c299de 100644
--- a/drivers/scsi/fcoe/fcoe.c
+++ b/drivers/scsi/fcoe/fcoe.c
@@ -2633,14 +2633,18 @@ static int __init fcoe_init(void)
                skb_queue_head_init(&p->fcoe_rx_list);
        }
 
+       cpu_maps_update_begin();
+
        for_each_online_cpu(cpu)
                fcoe_percpu_thread_create(cpu);
 
        /* Initialize per CPU interrupt thread */
-       rc = register_hotcpu_notifier(&fcoe_cpu_notifier);
+       rc = __register_hotcpu_notifier(&fcoe_cpu_notifier);
        if (rc)
                goto out_free;
 
+       cpu_maps_update_done();
+
        /* Setup link change notification */
        fcoe_dev_setup();
 
@@ -2655,6 +2659,9 @@ out_free:
        for_each_online_cpu(cpu) {
                fcoe_percpu_thread_destroy(cpu);
        }
+
+       cpu_maps_update_done();
+
        mutex_unlock(&fcoe_config_mutex);
        destroy_workqueue(fcoe_wq);
        return rc;
@@ -2687,11 +2694,15 @@ static void __exit fcoe_exit(void)
        }
        rtnl_unlock();
 
-       unregister_hotcpu_notifier(&fcoe_cpu_notifier);
+       cpu_maps_update_begin();
 
        for_each_online_cpu(cpu)
                fcoe_percpu_thread_destroy(cpu);
 
+       __unregister_hotcpu_notifier(&fcoe_cpu_notifier);
+
+       cpu_maps_update_done();
+
        mutex_unlock(&fcoe_config_mutex);
 
        /*

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