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powercap, intel-rapl: Fix CPU hotplug callback registration

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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_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>
This commit is contained in:
Srivatsa S. Bhat 2014-03-11 02:09:26 +05:30 committed by Rafael J. Wysocki
parent 4b0b68af37
commit 009f225ef0
1 changed files with 8 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
drivers/powercap/intel_rapl.c
View File

@ -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);