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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: Steven Rostedt <rostedt@goodmis.org>
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 02:11:56 +05:30 committed by Rafael J. Wysocki
parent 43ea953649
commit d39ad278a3
1 changed files with 11 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
kernel/trace/ring_buffer.c
View File

@ -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);