On Tue, 11 Mar 2014 02:09:26 +0530
"Srivatsa S. Bhat" <srivatsa.b...@linux.vnet.ibm.com> wrote:
> 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 intel-rapl code in the powercap driver by using this latter
> form of callback registration. But retain the calls to
> get/put_online_cpus(), since they also protect the function
> rapl_cleanup_data(). By nesting get/put_online_cpus() *inside*
> cpu_notifier_register_begin/done(), we avoid the ABBA deadlock
> possibility mentioned above.
>
> Cc: "Rafael J. Wysocki" <r...@rjwysocki.net>
> Cc: Jacob Pan <jacob.jun....@linux.intel.com>
> Cc: Srinivas Pandruvada <srinivas.pandruv...@linux.intel.com>
> Cc: Ingo Molnar <mi...@kernel.org>
> Signed-off-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
> ---
>
Tested-by: Jacob Pan <jacob.jun....@linux.intel.com>
> drivers/powercap/intel_rapl.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/powercap/intel_rapl.c
> b/drivers/powercap/intel_rapl.c index 3c67683..d6c74c1 100644
> --- a/drivers/powercap/intel_rapl.c
> +++ b/drivers/powercap/intel_rapl.c
> @@ -1369,6 +1369,9 @@ static int __init rapl_init(void)
>
> return -ENODEV;
> }
> +
> + cpu_notifier_register_begin();
> +
> /* prevent CPU hotplug during detection */
> get_online_cpus();
> ret = rapl_detect_topology();
> @@ -1380,20 +1383,23 @@ static int __init rapl_init(void)
> ret = -ENODEV;
> goto done;
> }
> - register_hotcpu_notifier(&rapl_cpu_notifier);
> + __register_hotcpu_notifier(&rapl_cpu_notifier);
> done:
> put_online_cpus();
> + cpu_notifier_register_done();
>
> return ret;
> }
>
> static void __exit rapl_exit(void)
> {
> + cpu_notifier_register_begin();
> get_online_cpus();
> - unregister_hotcpu_notifier(&rapl_cpu_notifier);
> + __unregister_hotcpu_notifier(&rapl_cpu_notifier);
> rapl_unregister_powercap();
> rapl_cleanup_data();
> put_online_cpus();
> + cpu_notifier_register_done();
> }
>
> module_init(rapl_init);
>
[Jacob Pan]
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