[v3,47/52] trace, ring-buffer: Fix CPU hotplug callback registration

Commit Message

Srivatsa S. Bhat March 10, 2014, 8:41 p.m. UTC

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 <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Acked-by: Steven Rostedt <[e-mail]>
Signed-off-by: Srivatsa S. Bhat <[e-mail]>
---

 kernel/trace/ring_buffer.c |   19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)


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Patch

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index fc4da2d..c634868 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -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);