linux/kernel/trace/trace_functions.c
Steven Rostedt 5361499101 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: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-01-16 12:15:32 +01:00

152 lines
3.1 KiB
C

/*
* ring buffer based function tracer
*
* Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
* Copyright (C) 2008 Ingo Molnar <mingo@redhat.com>
*
* Based on code from the latency_tracer, that is:
*
* Copyright (C) 2004-2006 Ingo Molnar
* Copyright (C) 2004 William Lee Irwin III
*/
#include <linux/debugfs.h>
#include <linux/uaccess.h>
#include <linux/ftrace.h>
#include <linux/fs.h>
#include "trace.h"
static struct trace_array *func_trace;
static void start_function_trace(struct trace_array *tr)
{
tr->cpu = get_cpu();
tracing_reset_online_cpus(tr);
put_cpu();
tracing_start_cmdline_record();
tracing_start_function_trace();
}
static void stop_function_trace(struct trace_array *tr)
{
tracing_stop_function_trace();
tracing_stop_cmdline_record();
}
static int function_trace_init(struct trace_array *tr)
{
func_trace = tr;
start_function_trace(tr);
return 0;
}
static void function_trace_reset(struct trace_array *tr)
{
stop_function_trace(tr);
}
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
};
static __init int init_function_trace(void)
{
return register_tracer(&function_trace);
}
device_initcall(init_function_trace);