tracing: Add function-trace option to disable function tracing of latency tracers

Currently, the only way to stop the latency tracers from doing function
tracing is to fully disable the function tracer from the proc file
system:

  echo 0 > /proc/sys/kernel/ftrace_enabled

This is a big hammer approach as it disables function tracing for
all users. This includes kprobes, perf, stack tracer, etc.

Instead, create a function-trace option that the latency tracers can
check to determine if it should enable function tracing or not.
This option can be set or cleared even while the tracer is active
and the tracers will disable or enable function tracing depending
on how the option was set.

Instead of using the proc file, disable latency function tracing with

  echo 0 > /debug/tracing/options/function-trace

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Clark Williams <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 8aa53213201ff985e766b30541b243d9d93ead53..f90ca16afcf2401b90ec85f24fffa631b576632f 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -328,7 +328,7 @@ static inline void trace_access_lock_init(void)
 unsigned long trace_flags = TRACE_ITER_PRINT_PARENT | TRACE_ITER_PRINTK |
        TRACE_ITER_ANNOTATE | TRACE_ITER_CONTEXT_INFO | TRACE_ITER_SLEEP_TIME |
        TRACE_ITER_GRAPH_TIME | TRACE_ITER_RECORD_CMD | TRACE_ITER_OVERWRITE |
-       TRACE_ITER_IRQ_INFO | TRACE_ITER_MARKERS;
+       TRACE_ITER_IRQ_INFO | TRACE_ITER_MARKERS | TRACE_ITER_FUNCTION;
 
 /**
  * tracing_on - enable tracing buffers
@@ -635,6 +635,7 @@ static const char *trace_options[] = {
        "disable_on_free",
        "irq-info",
        "markers",
+       "function-trace",
        NULL
 };
 

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 0e430b401ab67f217eef5b5b00948cb1abefd47f..5cc52361bc9f934a319b081f71fd435de827103b 100644 (file)
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -867,6 +867,7 @@ enum trace_iterator_flags {
        TRACE_ITER_STOP_ON_FREE         = 0x400000,
        TRACE_ITER_IRQ_INFO             = 0x800000,
        TRACE_ITER_MARKERS              = 0x1000000,
+       TRACE_ITER_FUNCTION             = 0x2000000,
 };
 
 /*

diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index 5aa40ab72b5744240c8bda842b08deeb1e7403a8..b19d065a28cb44b303d74d1a2ec6b13a04ec734f 100644 (file)
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -33,6 +33,7 @@ enum {
 static int trace_type __read_mostly;
 
 static int save_flags;
+static bool function_enabled;
 
 static void stop_irqsoff_tracer(struct trace_array *tr, int graph);
 static int start_irqsoff_tracer(struct trace_array *tr, int graph);
@@ -528,15 +529,60 @@ void trace_preempt_off(unsigned long a0, unsigned long a1)
 }
 #endif /* CONFIG_PREEMPT_TRACER */
 
-static int start_irqsoff_tracer(struct trace_array *tr, int graph)
+static int register_irqsoff_function(int graph, int set)
 {
-       int ret = 0;
+       int ret;
 
-       if (!graph)
-               ret = register_ftrace_function(&trace_ops);
-       else
+       /* 'set' is set if TRACE_ITER_FUNCTION is about to be set */
+       if (function_enabled || (!set && !(trace_flags & TRACE_ITER_FUNCTION)))
+               return 0;
+
+       if (graph)
                ret = register_ftrace_graph(&irqsoff_graph_return,
                                            &irqsoff_graph_entry);
+       else
+               ret = register_ftrace_function(&trace_ops);
+
+       if (!ret)
+               function_enabled = true;
+
+       return ret;
+}
+
+static void unregister_irqsoff_function(int graph)
+{
+       if (!function_enabled)
+               return;
+
+       if (graph)
+               unregister_ftrace_graph();
+       else
+               unregister_ftrace_function(&trace_ops);
+
+       function_enabled = false;
+}
+
+static void irqsoff_function_set(int set)
+{
+       if (set)
+               register_irqsoff_function(is_graph(), 1);
+       else
+               unregister_irqsoff_function(is_graph());
+}
+
+static int irqsoff_flag_changed(struct tracer *tracer, u32 mask, int set)
+{
+       if (mask & TRACE_ITER_FUNCTION)
+               irqsoff_function_set(set);
+
+       return trace_keep_overwrite(tracer, mask, set);
+}
+
+static int start_irqsoff_tracer(struct trace_array *tr, int graph)
+{
+       int ret;
+
+       ret = register_irqsoff_function(graph, 0);
 
        if (!ret && tracing_is_enabled())
                tracer_enabled = 1;
@@ -550,10 +596,7 @@ static void stop_irqsoff_tracer(struct trace_array *tr, int graph)
 {
        tracer_enabled = 0;
 
-       if (!graph)
-               unregister_ftrace_function(&trace_ops);
-       else
-               unregister_ftrace_graph();
+       unregister_irqsoff_function(graph);
 }
 
 static void __irqsoff_tracer_init(struct trace_array *tr)
@@ -615,7 +658,7 @@ static struct tracer irqsoff_tracer __read_mostly =
        .print_line     = irqsoff_print_line,
        .flags          = &tracer_flags,
        .set_flag       = irqsoff_set_flag,
-       .flag_changed   = trace_keep_overwrite,
+       .flag_changed   = irqsoff_flag_changed,
 #ifdef CONFIG_FTRACE_SELFTEST
        .selftest    = trace_selftest_startup_irqsoff,
 #endif
@@ -649,7 +692,7 @@ static struct tracer preemptoff_tracer __read_mostly =
        .print_line     = irqsoff_print_line,
        .flags          = &tracer_flags,
        .set_flag       = irqsoff_set_flag,
-       .flag_changed   = trace_keep_overwrite,
+       .flag_changed   = irqsoff_flag_changed,
 #ifdef CONFIG_FTRACE_SELFTEST
        .selftest    = trace_selftest_startup_preemptoff,
 #endif
@@ -685,7 +728,7 @@ static struct tracer preemptirqsoff_tracer __read_mostly =
        .print_line     = irqsoff_print_line,
        .flags          = &tracer_flags,
        .set_flag       = irqsoff_set_flag,
-       .flag_changed   = trace_keep_overwrite,
+       .flag_changed   = irqsoff_flag_changed,
 #ifdef CONFIG_FTRACE_SELFTEST
        .selftest    = trace_selftest_startup_preemptirqsoff,
 #endif

diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
index c16f8cd63c3ca9237743a43e6b38667f1055d3a0..fee77e15d8154e5a9a7936824b14b6d805c0dc13 100644 (file)
--- a/kernel/trace/trace_sched_wakeup.c
+++ b/kernel/trace/trace_sched_wakeup.c
@@ -37,6 +37,7 @@ static int wakeup_graph_entry(struct ftrace_graph_ent *trace);
 static void wakeup_graph_return(struct ftrace_graph_ret *trace);
 
 static int save_flags;
+static bool function_enabled;
 
 #define TRACE_DISPLAY_GRAPH     1
 
@@ -134,15 +135,60 @@ static struct ftrace_ops trace_ops __read_mostly =
 };
 #endif /* CONFIG_FUNCTION_TRACER */
 
-static int start_func_tracer(int graph)
+static int register_wakeup_function(int graph, int set)
 {
        int ret;
 
-       if (!graph)
-               ret = register_ftrace_function(&trace_ops);
-       else
+       /* 'set' is set if TRACE_ITER_FUNCTION is about to be set */
+       if (function_enabled || (!set && !(trace_flags & TRACE_ITER_FUNCTION)))
+               return 0;
+
+       if (graph)
                ret = register_ftrace_graph(&wakeup_graph_return,
                                            &wakeup_graph_entry);
+       else
+               ret = register_ftrace_function(&trace_ops);
+
+       if (!ret)
+               function_enabled = true;
+
+       return ret;
+}
+
+static void unregister_wakeup_function(int graph)
+{
+       if (!function_enabled)
+               return;
+
+       if (graph)
+               unregister_ftrace_graph();
+       else
+               unregister_ftrace_function(&trace_ops);
+
+       function_enabled = false;
+}
+
+static void wakeup_function_set(int set)
+{
+       if (set)
+               register_wakeup_function(is_graph(), 1);
+       else
+               unregister_wakeup_function(is_graph());
+}
+
+static int wakeup_flag_changed(struct tracer *tracer, u32 mask, int set)
+{
+       if (mask & TRACE_ITER_FUNCTION)
+               wakeup_function_set(set);
+
+       return trace_keep_overwrite(tracer, mask, set);
+}
+
+static int start_func_tracer(int graph)
+{
+       int ret;
+
+       ret = register_wakeup_function(graph, 0);
 
        if (!ret && tracing_is_enabled())
                tracer_enabled = 1;
@@ -156,10 +202,7 @@ static void stop_func_tracer(int graph)
 {
        tracer_enabled = 0;
 
-       if (!graph)
-               unregister_ftrace_function(&trace_ops);
-       else
-               unregister_ftrace_graph();
+       unregister_wakeup_function(graph);
 }
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
@@ -600,7 +643,7 @@ static struct tracer wakeup_tracer __read_mostly =
        .print_line     = wakeup_print_line,
        .flags          = &tracer_flags,
        .set_flag       = wakeup_set_flag,
-       .flag_changed   = trace_keep_overwrite,
+       .flag_changed   = wakeup_flag_changed,
 #ifdef CONFIG_FTRACE_SELFTEST
        .selftest    = trace_selftest_startup_wakeup,
 #endif
@@ -622,7 +665,7 @@ static struct tracer wakeup_rt_tracer __read_mostly =
        .print_line     = wakeup_print_line,
        .flags          = &tracer_flags,
        .set_flag       = wakeup_set_flag,
-       .flag_changed   = trace_keep_overwrite,
+       .flag_changed   = wakeup_flag_changed,
 #ifdef CONFIG_FTRACE_SELFTEST
        .selftest    = trace_selftest_startup_wakeup,
 #endif