linux-kernel - [PATCH] trace: ftrace: remove ftrace_cpu

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Date:	Fri,  6 Nov 2015 22:07:26 +0300
From:	Dmitry Safonov <0x7f454c46@...il.com>
To:	rostedt@...dmis.org, mingo@...hat.com
Cc:	linux-kernel@...r.kernel.org, Dmitry Safonov <0x7f454c46@...il.com>
Subject: [PATCH] trace: ftrace: remove ftrace_cpu_disabled

Since the ring buffer is lockless, there is no need to disable ftrace on
CPU. And no one doing so: after commit 68179686ac67cb ("tracing: Remove
ftrace_disable/enable_cpu()") ftrace_cpu_disabled stays the same after
initialization, nothing changes it.
ftrace_cpu_disabled shouldn't be used by any external module since it
disables only function and graph_function tracers but not any other
tracer.

Signed-off-by: Dmitry Safonov <0x7f454c46@...il.com>
---
 kernel/trace/trace.c                 | 6 ------
 kernel/trace/trace.h                 | 1 -
 kernel/trace/trace_functions_graph.c | 6 ------
 3 files changed, 13 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 6e79408674aaa1..0bc15c53eaee29 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -100,8 +100,6 @@ static DEFINE_PER_CPU(bool, trace_cmdline_save);
  */
 static int tracing_disabled = 1;
 
-DEFINE_PER_CPU(int, ftrace_cpu_disabled);
-
 cpumask_var_t __read_mostly	tracing_buffer_mask;
 
 /*
@@ -1766,10 +1764,6 @@ trace_function(struct trace_array *tr,
 	struct ring_buffer_event *event;
 	struct ftrace_entry *entry;
 
-	/* If we are reading the ring buffer, don't trace */
-	if (unlikely(__this_cpu_read(ftrace_cpu_disabled)))
-		return;
-
 	event = trace_buffer_lock_reserve(buffer, TRACE_FN, sizeof(*entry),
 					  flags, pc);
 	if (!event)
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 74bde81601a902..70ab82374d05fd 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -659,7 +659,6 @@ extern int DYN_FTRACE_TEST_NAME2(void);
 
 extern bool ring_buffer_expanded;
 extern bool tracing_selftest_disabled;
-DECLARE_PER_CPU(int, ftrace_cpu_disabled);
 
 #ifdef CONFIG_FTRACE_STARTUP_TEST
 extern int trace_selftest_startup_function(struct tracer *trace,
diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index ca98445782acaa..266e95886c50f2 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -283,9 +283,6 @@ int __trace_graph_entry(struct trace_array *tr,
 	struct ring_buffer *buffer = tr->trace_buffer.buffer;
 	struct ftrace_graph_ent_entry *entry;
 
-	if (unlikely(__this_cpu_read(ftrace_cpu_disabled)))
-		return 0;
-
 	event = trace_buffer_lock_reserve(buffer, TRACE_GRAPH_ENT,
 					  sizeof(*entry), flags, pc);
 	if (!event)
@@ -398,9 +395,6 @@ void __trace_graph_return(struct trace_array *tr,
 	struct ring_buffer *buffer = tr->trace_buffer.buffer;
 	struct ftrace_graph_ret_entry *entry;
 
-	if (unlikely(__this_cpu_read(ftrace_cpu_disabled)))
-		return;
-
 	event = trace_buffer_lock_reserve(buffer, TRACE_GRAPH_RET,
 					  sizeof(*entry), flags, pc);
 	if (!event)
-- 
2.6.2

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