| From | "Srivatsa S. Bhat" <> | Subject | [PATCH 30/51] powercap, intel-rapl: Fix CPU hotplug callback registration | Date | Thu, 06 Feb 2014 03:40:07 +0530 |
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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 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_maps_update_begin/done(), we avoid the ABBA deadlock possibility mentioned above.
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com> Cc: Jacob Pan <jacob.jun.pan@linux.intel.com> Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.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..b460d46 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_maps_update_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_maps_update_done(); return ret; } static void __exit rapl_exit(void) { + cpu_maps_update_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_maps_update_done(); } module_init(rapl_init);
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