Commit 53614991 authored by Steven Rostedt's avatar Steven Rostedt Committed by Ingo Molnar
Browse files

ftrace: add stack trace to function tracer 



Impact: new feature to stack trace any function

Chris Mason asked about being able to pick and choose a function
and get a stack trace from it. This feature enables his request.

 # echo io_schedule > /debug/tracing/set_ftrace_filter
 # echo function > /debug/tracing/current_tracer
 # echo func_stack_trace > /debug/tracing/trace_options

Produces the following in /debug/tracing/trace:

       kjournald-702   [001]   135.673060: io_schedule <-sync_buffer
       kjournald-702   [002]   135.673671:
 <= sync_buffer
 <= __wait_on_bit
 <= out_of_line_wait_on_bit
 <= __wait_on_buffer
 <= sync_dirty_buffer
 <= journal_commit_transaction
 <= kjournald

Note, be careful about turning this on without filtering the functions.
You may find that you have a 10 second lag between typing and seeing
what you typed. This is why the stack trace for the function tracer
does not use the same stack_trace flag as the other tracers use.

Signed-off-by: default avatarSteven Rostedt <srostedt@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 6c1a99af

kernel/trace/trace.c

+17 −9
Original line number Diff line number Diff line
@@ -835,7 +835,7 @@ ftrace(struct trace_array *tr, struct trace_array_cpu *data, 
		trace_function(tr, data, ip, parent_ip, flags, pc);

}



static void ftrace_trace_stack(struct trace_array *tr,

static void __ftrace_trace_stack(struct trace_array *tr,

				 struct trace_array_cpu *data,

				 unsigned long flags,

				 int skip, int pc)
@@ -846,9 +846,6 @@ static void ftrace_trace_stack(struct trace_array *tr, 
	struct stack_trace trace;

	unsigned long irq_flags;



	if (!(trace_flags & TRACE_ITER_STACKTRACE))

		return;



	event = ring_buffer_lock_reserve(tr->buffer, sizeof(*entry),

					 &irq_flags);

	if (!event)
@@ -869,12 +866,23 @@ static void ftrace_trace_stack(struct trace_array *tr, 
#endif

}



static void ftrace_trace_stack(struct trace_array *tr,

			       struct trace_array_cpu *data,

			       unsigned long flags,

			       int skip, int pc)

{

	if (!(trace_flags & TRACE_ITER_STACKTRACE))

		return;



	__ftrace_trace_stack(tr, data, flags, skip, pc);

}



void __trace_stack(struct trace_array *tr,

		   struct trace_array_cpu *data,

		   unsigned long flags,

		   int skip)

		   int skip, int pc)

{

	ftrace_trace_stack(tr, data, flags, skip, preempt_count());

	__ftrace_trace_stack(tr, data, flags, skip, pc);

}



static void ftrace_trace_userstack(struct trace_array *tr,

kernel/trace/trace.h

+7 −0
Original line number Diff line number Diff line
@@ -457,6 +457,11 @@ void update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu); 
void update_max_tr_single(struct trace_array *tr,

			  struct task_struct *tsk, int cpu);



void __trace_stack(struct trace_array *tr,

		   struct trace_array_cpu *data,

		   unsigned long flags,

		   int skip, int pc);



extern cycle_t ftrace_now(int cpu);



#ifdef CONFIG_FUNCTION_TRACER
@@ -467,6 +472,8 @@ void tracing_stop_function_trace(void); 
# define tracing_stop_function_trace()		do { } while (0)

#endif



extern int ftrace_function_enabled;



#ifdef CONFIG_CONTEXT_SWITCH_TRACER

typedef void

(*tracer_switch_func_t)(void *private,

kernel/trace/trace_functions.c

+84 −0
Original line number Diff line number Diff line
@@ -16,6 +16,8 @@ 


#include "trace.h"



static struct trace_array	*func_trace;



static void start_function_trace(struct trace_array *tr)

{

	tr->cpu = get_cpu();
@@ -34,6 +36,7 @@ static void stop_function_trace(struct trace_array *tr) 


static int function_trace_init(struct trace_array *tr)

{

	func_trace = tr;

	start_function_trace(tr);

	return 0;

}
@@ -48,12 +51,93 @@ static void function_trace_start(struct trace_array *tr) 
	tracing_reset_online_cpus(tr);

}



static void

function_stack_trace_call(unsigned long ip, unsigned long parent_ip)

{

	struct trace_array *tr = func_trace;

	struct trace_array_cpu *data;

	unsigned long flags;

	long disabled;

	int cpu;

	int pc;



	if (unlikely(!ftrace_function_enabled))

		return;



	/*

	 * Need to use raw, since this must be called before the

	 * recursive protection is performed.

	 */

	local_irq_save(flags);

	cpu = raw_smp_processor_id();

	data = tr->data[cpu];

	disabled = atomic_inc_return(&data->disabled);



	if (likely(disabled == 1)) {

		pc = preempt_count();

		/*

		 * skip over 5 funcs:

		 *    __ftrace_trace_stack,

		 *    __trace_stack,

		 *    function_stack_trace_call

		 *    ftrace_list_func

		 *    ftrace_call

		 */

		__trace_stack(tr, data, flags, 5, pc);

	}



	atomic_dec(&data->disabled);

	local_irq_restore(flags);

}



static struct ftrace_ops trace_stack_ops __read_mostly =

{

	.func = function_stack_trace_call,

};



/* Our two options */

enum {

	TRACE_FUNC_OPT_STACK = 0x1,

};



static struct tracer_opt func_opts[] = {

#ifdef CONFIG_STACKTRACE

	{ TRACER_OPT(func_stack_trace, TRACE_FUNC_OPT_STACK) },

#endif

	{ } /* Always set a last empty entry */

};



static struct tracer_flags func_flags = {

	.val = 0, /* By default: all flags disabled */

	.opts = func_opts

};



static int func_set_flag(u32 old_flags, u32 bit, int set)

{

	if (bit == TRACE_FUNC_OPT_STACK) {

		/* do nothing if already set */

		if (!!set == !!(func_flags.val & TRACE_FUNC_OPT_STACK))

			return 0;



		if (set)

			register_ftrace_function(&trace_stack_ops);

		else

			unregister_ftrace_function(&trace_stack_ops);



		return 0;

	}



	return -EINVAL;

}



static struct tracer function_trace __read_mostly =

{

	.name	     = "function",

	.init	     = function_trace_init,

	.reset	     = function_trace_reset,

	.start	     = function_trace_start,

	.flags		= &func_flags,

	.set_flag	= func_set_flag,

#ifdef CONFIG_FTRACE_SELFTEST

	.selftest    = trace_selftest_startup_function,

#endif

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