Re: [PATCH v3 32/52] powercap, intel-rapl: Fix CPU hotplug callback registration
From: Jacob Pan <hidden>
Date: 2014-03-12 22:28:47
Also in:
linux-arch, linux-pm, lkml
On Tue, 11 Mar 2014 02:09:26 +0530 "Srivatsa S. Bhat" [off-list ref] 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" <redacted> Cc: Jacob Pan <redacted> Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> Cc: Ingo Molnar <mingo@kernel.org> Signed-off-by: Srivatsa S. Bhat <redacted> ---
Tested-by: Jacob Pan <redacted>
quoted hunk ↗ jump to hunk
drivers/powercap/intel_rapl.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)diff --git a/drivers/powercap/intel_rapl.cb/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]