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Commit d39ad278 authored by Srivatsa S. Bhat's avatar Srivatsa S. Bhat Committed by Rafael J. Wysocki
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trace, ring-buffer: 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 tracing ring-buffer code by using this latter form of callback
registration.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Acked-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 43ea9536

kernel/trace/ring_buffer.c

+11 −8
Original line number Diff line number Diff line
@@ -1301,7 +1301,7 @@ struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags, 
	 * In that off case, we need to allocate for all possible cpus.

	 */

#ifdef CONFIG_HOTPLUG_CPU

	get_online_cpus();

	cpu_notifier_register_begin();

	cpumask_copy(buffer->cpumask, cpu_online_mask);

#else

	cpumask_copy(buffer->cpumask, cpu_possible_mask);
@@ -1324,10 +1324,10 @@ struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags, 
#ifdef CONFIG_HOTPLUG_CPU

	buffer->cpu_notify.notifier_call = rb_cpu_notify;

	buffer->cpu_notify.priority = 0;

	register_cpu_notifier(&buffer->cpu_notify);

	__register_cpu_notifier(&buffer->cpu_notify);

	cpu_notifier_register_done();

#endif



	put_online_cpus();

	mutex_init(&buffer->mutex);



	return buffer;
@@ -1341,7 +1341,9 @@ struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags, 


 fail_free_cpumask:

	free_cpumask_var(buffer->cpumask);

	put_online_cpus();

#ifdef CONFIG_HOTPLUG_CPU

	cpu_notifier_register_done();

#endif



 fail_free_buffer:

	kfree(buffer);
@@ -1358,16 +1360,17 @@ ring_buffer_free(struct ring_buffer *buffer) 
{

	int cpu;



	get_online_cpus();



#ifdef CONFIG_HOTPLUG_CPU

	unregister_cpu_notifier(&buffer->cpu_notify);

	cpu_notifier_register_begin();

	__unregister_cpu_notifier(&buffer->cpu_notify);

#endif



	for_each_buffer_cpu(buffer, cpu)

		rb_free_cpu_buffer(buffer->buffers[cpu]);



	put_online_cpus();

#ifdef CONFIG_HOTPLUG_CPU

	cpu_notifier_register_done();

#endif



	kfree(buffer->buffers);

	free_cpumask_var(buffer->cpumask);