linux-hardened/kernel/trace/trace_functions.c
Frederic Weisbecker c85a17e226 tracing/urgent: fix unbalanced ftrace_start_up
Perfcounter reports the following stats for a wide system
profiling:

 #
 # (2364 samples)
 #
 # Overhead  Symbol
 # ........  ......
 #
    15.40%  [k] mwait_idle_with_hints
     8.29%  [k] read_hpet
     5.75%  [k] ftrace_caller
     3.60%  [k] ftrace_call
     [...]

This snapshot has been taken while neither the function tracer nor
the function graph tracer was running.
With dynamic ftrace, such results show a wrong ftrace behaviour
because all calls to ftrace_caller or ftrace_graph_caller (the patched
calls to mcount) are supposed to be patched into nop if none of those
tracers are running.

The problem occurs after the first run of the function tracer. Once we
launch it a second time, the callsites will never be nopped back,
unless you set custom filters.
For example it happens during the self tests at boot time.
The function tracer selftest runs, and then the dynamic tracing is
tested too. After that, the callsites are left un-nopped.

This is because the reset callback of the function tracer tries to
unregister two ftrace callbacks in once: the common function tracer
and the function tracer with stack backtrace, regardless of which
one is currently in use.
It then creates an unbalance on ftrace_start_up value which is expected
to be zero when the last ftrace callback is unregistered. When it
reaches zero, the FTRACE_DISABLE_CALLS is set on the next ftrace
command, triggering the patching into nop. But since it becomes
unbalanced, ie becomes lower than zero, if the kernel functions
are patched again (as in every further function tracer runs), they
won't ever be nopped back.

Note that ftrace_call and ftrace_graph_call are still patched back
to ftrace_stub in the off case, but not the callers of ftrace_call
and ftrace_graph_caller. It means that the tracing is well deactivated
but we waste a useless call into every kernel function.

This patch just unregisters the right ftrace_ops for the function
tracer on its reset callback and ignores the other one which is
not registered, fixing the unbalance. The problem also happens
is .30

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: stable@kernel.org
2009-06-20 06:28:46 +02:00

406 lines
8.2 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/ring_buffer.h>
#include <linux/debugfs.h>
#include <linux/uaccess.h>
#include <linux/ftrace.h>
#include <linux/fs.h>
#include "trace.h"
/* function tracing enabled */
static int ftrace_function_enabled;
static struct trace_array *func_trace;
static void tracing_start_function_trace(void);
static void tracing_stop_function_trace(void);
static int function_trace_init(struct trace_array *tr)
{
func_trace = tr;
tr->cpu = get_cpu();
put_cpu();
tracing_start_cmdline_record();
tracing_start_function_trace();
return 0;
}
static void function_trace_reset(struct trace_array *tr)
{
tracing_stop_function_trace();
tracing_stop_cmdline_record();
}
static void function_trace_start(struct trace_array *tr)
{
tracing_reset_online_cpus(tr);
}
static void
function_trace_call_preempt_only(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, resched;
int pc;
if (unlikely(!ftrace_function_enabled))
return;
pc = preempt_count();
resched = ftrace_preempt_disable();
local_save_flags(flags);
cpu = raw_smp_processor_id();
data = tr->data[cpu];
disabled = atomic_inc_return(&data->disabled);
if (likely(disabled == 1))
trace_function(tr, ip, parent_ip, flags, pc);
atomic_dec(&data->disabled);
ftrace_preempt_enable(resched);
}
static void
function_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();
trace_function(tr, ip, parent_ip, flags, pc);
}
atomic_dec(&data->disabled);
local_irq_restore(flags);
}
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();
trace_function(tr, ip, parent_ip, flags, pc);
/*
* skip over 5 funcs:
* __ftrace_trace_stack,
* __trace_stack,
* function_stack_trace_call
* ftrace_list_func
* ftrace_call
*/
__trace_stack(tr, flags, 5, pc);
}
atomic_dec(&data->disabled);
local_irq_restore(flags);
}
static struct ftrace_ops trace_ops __read_mostly =
{
.func = function_trace_call,
};
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 void tracing_start_function_trace(void)
{
ftrace_function_enabled = 0;
if (trace_flags & TRACE_ITER_PREEMPTONLY)
trace_ops.func = function_trace_call_preempt_only;
else
trace_ops.func = function_trace_call;
if (func_flags.val & TRACE_FUNC_OPT_STACK)
register_ftrace_function(&trace_stack_ops);
else
register_ftrace_function(&trace_ops);
ftrace_function_enabled = 1;
}
static void tracing_stop_function_trace(void)
{
ftrace_function_enabled = 0;
if (func_flags.val & TRACE_FUNC_OPT_STACK)
unregister_ftrace_function(&trace_stack_ops);
else
unregister_ftrace_function(&trace_ops);
}
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) {
unregister_ftrace_function(&trace_ops);
register_ftrace_function(&trace_stack_ops);
} else {
unregister_ftrace_function(&trace_stack_ops);
register_ftrace_function(&trace_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,
.wait_pipe = poll_wait_pipe,
.flags = &func_flags,
.set_flag = func_set_flag,
#ifdef CONFIG_FTRACE_SELFTEST
.selftest = trace_selftest_startup_function,
#endif
};
#ifdef CONFIG_DYNAMIC_FTRACE
static void
ftrace_traceon(unsigned long ip, unsigned long parent_ip, void **data)
{
long *count = (long *)data;
if (tracing_is_on())
return;
if (!*count)
return;
if (*count != -1)
(*count)--;
tracing_on();
}
static void
ftrace_traceoff(unsigned long ip, unsigned long parent_ip, void **data)
{
long *count = (long *)data;
if (!tracing_is_on())
return;
if (!*count)
return;
if (*count != -1)
(*count)--;
tracing_off();
}
static int
ftrace_trace_onoff_print(struct seq_file *m, unsigned long ip,
struct ftrace_probe_ops *ops, void *data);
static struct ftrace_probe_ops traceon_probe_ops = {
.func = ftrace_traceon,
.print = ftrace_trace_onoff_print,
};
static struct ftrace_probe_ops traceoff_probe_ops = {
.func = ftrace_traceoff,
.print = ftrace_trace_onoff_print,
};
static int
ftrace_trace_onoff_print(struct seq_file *m, unsigned long ip,
struct ftrace_probe_ops *ops, void *data)
{
char str[KSYM_SYMBOL_LEN];
long count = (long)data;
kallsyms_lookup(ip, NULL, NULL, NULL, str);
seq_printf(m, "%s:", str);
if (ops == &traceon_probe_ops)
seq_printf(m, "traceon");
else
seq_printf(m, "traceoff");
if (count == -1)
seq_printf(m, ":unlimited\n");
else
seq_printf(m, ":count=%ld", count);
seq_putc(m, '\n');
return 0;
}
static int
ftrace_trace_onoff_unreg(char *glob, char *cmd, char *param)
{
struct ftrace_probe_ops *ops;
/* we register both traceon and traceoff to this callback */
if (strcmp(cmd, "traceon") == 0)
ops = &traceon_probe_ops;
else
ops = &traceoff_probe_ops;
unregister_ftrace_function_probe_func(glob, ops);
return 0;
}
static int
ftrace_trace_onoff_callback(char *glob, char *cmd, char *param, int enable)
{
struct ftrace_probe_ops *ops;
void *count = (void *)-1;
char *number;
int ret;
/* hash funcs only work with set_ftrace_filter */
if (!enable)
return -EINVAL;
if (glob[0] == '!')
return ftrace_trace_onoff_unreg(glob+1, cmd, param);
/* we register both traceon and traceoff to this callback */
if (strcmp(cmd, "traceon") == 0)
ops = &traceon_probe_ops;
else
ops = &traceoff_probe_ops;
if (!param)
goto out_reg;
number = strsep(&param, ":");
if (!strlen(number))
goto out_reg;
/*
* We use the callback data field (which is a pointer)
* as our counter.
*/
ret = strict_strtoul(number, 0, (unsigned long *)&count);
if (ret)
return ret;
out_reg:
ret = register_ftrace_function_probe(glob, ops, count);
return ret;
}
static struct ftrace_func_command ftrace_traceon_cmd = {
.name = "traceon",
.func = ftrace_trace_onoff_callback,
};
static struct ftrace_func_command ftrace_traceoff_cmd = {
.name = "traceoff",
.func = ftrace_trace_onoff_callback,
};
static int __init init_func_cmd_traceon(void)
{
int ret;
ret = register_ftrace_command(&ftrace_traceoff_cmd);
if (ret)
return ret;
ret = register_ftrace_command(&ftrace_traceon_cmd);
if (ret)
unregister_ftrace_command(&ftrace_traceoff_cmd);
return ret;
}
#else
static inline int init_func_cmd_traceon(void)
{
return 0;
}
#endif /* CONFIG_DYNAMIC_FTRACE */
static __init int init_function_trace(void)
{
init_func_cmd_traceon();
return register_tracer(&function_trace);
}
device_initcall(init_function_trace);