[PATCH v2 08/52] ia64, err-inject: 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_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 error injection code in ia64 by using this latter form of callback
registration.

Cc: Tony Luck <tony.l...@intel.com>
Cc: Fenghua Yu <fenghua...@intel.com>
Cc: Ingo Molnar <mi...@kernel.org>
Cc: linux-i...@vger.kernel.org
Signed-off-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
---

 arch/ia64/kernel/err_inject.c |   15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/ia64/kernel/err_inject.c b/arch/ia64/kernel/err_inject.c
index f59c0b8..0c161ed 100644
--- a/arch/ia64/kernel/err_inject.c
+++ b/arch/ia64/kernel/err_inject.c
@@ -269,12 +269,17 @@ err_inject_init(void)
 #ifdef ERR_INJ_DEBUG
        printk(KERN_INFO "Enter error injection driver.\n");
 #endif
+
+       cpu_notifier_register_begin();
+
        for_each_online_cpu(i) {
                err_inject_cpu_callback(&err_inject_cpu_notifier, CPU_ONLINE,
                                (void *)(long)i);
        }
 
-       register_hotcpu_notifier(&err_inject_cpu_notifier);
+       __register_hotcpu_notifier(&err_inject_cpu_notifier);
+
+       cpu_notifier_register_done();
 
        return 0;
 }
@@ -288,11 +293,17 @@ err_inject_exit(void)
 #ifdef ERR_INJ_DEBUG
        printk(KERN_INFO "Exit error injection driver.\n");
 #endif
+
+       cpu_notifier_register_begin();
+
        for_each_online_cpu(i) {
                sys_dev = get_cpu_device(i);
                sysfs_remove_group(&sys_dev->kobj, &err_inject_attr_group);
        }
-       unregister_hotcpu_notifier(&err_inject_cpu_notifier);
+
+       __unregister_hotcpu_notifier(&err_inject_cpu_notifier);
+
+       cpu_notifier_register_done();
 }
 
 module_init(err_inject_init);

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