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authorSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>2014-03-11 02:09:26 +0530
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2014-03-20 13:43:44 +0100
commit009f225ef050d231ebb7b87264a21a7daac0f175 (patch)
tree520aab509ac35b0030ad955fa976f6108e666c2c /drivers/powercap/intel_rapl.c
parent4b0b68af37b930403cf9074c0cf504fc2387c2fa (diff)
powercap, intel-rapl: Fix CPU hotplug callback registration
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: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> Cc: Ingo Molnar <mingo@kernel.org> Tested-by: Jacob Pan <jacob.jun.pan@linux.intel.com> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'drivers/powercap/intel_rapl.c')
-rw-r--r--drivers/powercap/intel_rapl.c10
1 files changed, 8 insertions, 2 deletions
diff --git a/drivers/powercap/intel_rapl.c b/drivers/powercap/intel_rapl.c
index 3c6768378a94..d6c74c1b5ea7 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);