| Message ID | 20140310203926.10746.11524.stgit@srivatsabhat.in.ibm.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
On Tue, 11 Mar 2014 02:09:26 +0530 "Srivatsa S. Bhat" <srivatsa.bhat@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" <rjw@rjwysocki.net> > Cc: Jacob Pan <jacob.jun.pan@linux.intel.com> > Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> > Cc: Ingo Molnar <mingo@kernel.org> > Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> > --- > Tested-by: Jacob Pan <jacob.jun.pan@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]
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);
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" <rjw@rjwysocki.net> Cc: Jacob Pan <jacob.jun.pan@linux.intel.com> Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> Cc: Ingo Molnar <mingo@kernel.org> 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(-)