[PATCH v4 4/4] trace: change CPU ring buffer state from tracing_cpumask

[Vaibhav Nagarnaik <vnagarnaik@google.com>]

According to Documentation/trace/ftrace.txt:

tracing_cpumask:

        This is a mask that lets the user only trace
        on specified CPUS. The format is a hex string
        representing the CPUS.

The tracing_cpumask currently doesn't affect the tracing state of
per-CPU ring buffers.

This patch enables/disables CPU recording as its corresponding bit in
tracing_cpumask is set/unset.

Signed-off-by: Vaibhav Nagarnaik <vnagarnaik@google.com>
---
 kernel/trace/trace.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 736518f..a8999bd 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2529,10 +2529,12 @@ tracing_cpumask_write(struct file *filp, const char __user *ubuf,
 		if (cpumask_test_cpu(cpu, tracing_cpumask) &&
 				!cpumask_test_cpu(cpu, tracing_cpumask_new)) {
 			atomic_inc(&global_trace.data[cpu]->disabled);
+			ring_buffer_record_disable_cpu(global_trace.buffer, cpu);
 		}
 		if (!cpumask_test_cpu(cpu, tracing_cpumask) &&
 				cpumask_test_cpu(cpu, tracing_cpumask_new)) {
 			atomic_dec(&global_trace.data[cpu]->disabled);
+			ring_buffer_record_enable_cpu(global_trace.buffer, cpu);
 		}
 	}
 	arch_spin_unlock(&ftrace_max_lock);
-- 
1.7.3.1