trace: let boot trace be chosen by command line

Now that we have a working ftrace=<tracer> function, make the boot
tracer get activated by it. This way we can turn it on or off without
recompiling the kernel, as well as keeping the selftests on. The
selftests are disabled whenever a default tracer starts running.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 11 insertions, 12 deletions

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index dde1d46f77e5..28f2644484d9 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -164,9 +164,8 @@ config BOOT_TRACER
           representation of the delays during initcalls - but the raw
           /debug/tracing/trace text output is readable too.
 
-          ( Note that tracing self tests can't be enabled if this tracer is
-            selected, because the self-tests are an initcall as well and that
-            would invalidate the boot trace. )
+          You must pass in ftrace=initcall to the kernel command line
+          to enable this on bootup.
 
 config TRACE_BRANCH_PROFILING
         bool "Trace likely/unlikely profiler"
@@ -326,7 +325,7 @@ config FTRACE_SELFTEST
 
 config FTRACE_STARTUP_TEST
         bool "Perform a startup test on ftrace"
-        depends on TRACING && DEBUG_KERNEL && !BOOT_TRACER
+        depends on TRACING && DEBUG_KERNEL
         select FTRACE_SELFTEST
         help
           This option performs a series of startup tests on ftrace. On bootup
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 2c720c79bc60..40edef4255c5 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3167,12 +3167,9 @@ __init static int tracer_alloc_buffers(void)
         trace_init_cmdlines();
 
         register_tracer(&nop_trace);
+        current_trace = &nop_trace;
 #ifdef CONFIG_BOOT_TRACER
         register_tracer(&boot_tracer);
-        current_trace = &boot_tracer;
-        current_trace->init(&global_trace);
-#else
-        current_trace = &nop_trace;
 #endif
         /* All seems OK, enable tracing */
         tracing_disabled = 0;
diff --git a/kernel/trace/trace_boot.c b/kernel/trace/trace_boot.c
index 0e94b3d091f7..1f07895977a0 100644
--- a/kernel/trace/trace_boot.c
+++ b/kernel/trace/trace_boot.c
@@ -28,13 +28,13 @@ void start_boot_trace(void)
 
 void enable_boot_trace(void)
 {
-        if (pre_initcalls_finished)
+        if (boot_trace && pre_initcalls_finished)
                 tracing_start_sched_switch_record();
 }
 
 void disable_boot_trace(void)
 {
-        if (pre_initcalls_finished)
+        if (boot_trace && pre_initcalls_finished)
                 tracing_stop_sched_switch_record();
 }
 
@@ -43,6 +43,9 @@ static int boot_trace_init(struct trace_array *tr)
         int cpu;
         boot_trace = tr;
 
+        if (!tr)
+                return 0;
+
         for_each_cpu(cpu, cpu_possible_mask)
                 tracing_reset(tr, cpu);
 
@@ -132,7 +135,7 @@ void trace_boot_call(struct boot_trace_call *bt, initcall_t fn)
         unsigned long irq_flags;
         struct trace_array *tr = boot_trace;
 
-        if (!pre_initcalls_finished)
+        if (!tr || !pre_initcalls_finished)
                 return;
 
         /* Get its name now since this function could
@@ -164,7 +167,7 @@ void trace_boot_ret(struct boot_trace_ret *bt, initcall_t fn)
         unsigned long irq_flags;
         struct trace_array *tr = boot_trace;
 
-        if (!pre_initcalls_finished)
+        if (!tr || !pre_initcalls_finished)
                 return;
 
         sprint_symbol(bt->func, (unsigned long)fn);