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ftrace: add ftrace_enabled sysctl to disable mcount function
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This patch adds back the sysctl ftrace_enabled. This time it is
defaulted to on, if DYNAMIC_FTRACE is configured. When ftrace_enabled
is disabled, the ftrace function is set to the stub return.

If DYNAMIC_FTRACE is also configured, on ftrace_enabled = 0,
the registered ftrace functions will all be set to jmps, but no more
new calls to ftrace recording (used to find the ftrace calling sites)
will be called.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Steven Rostedt authored and Thomas Gleixner committed May 23, 2008
1 parent 3d08339 commit b0fc494
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Showing 3 changed files with 124 additions and 18 deletions.
6 changes: 6 additions & 0 deletions include/linux/ftrace.h
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,12 @@

#include <linux/linkage.h>

extern int ftrace_enabled;
extern int
ftrace_enable_sysctl(struct ctl_table *table, int write,
struct file *filp, void __user *buffer, size_t *lenp,
loff_t *ppos);

typedef void (*ftrace_func_t)(unsigned long ip, unsigned long parent_ip);

struct ftrace_ops {
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11 changes: 11 additions & 0 deletions kernel/sysctl.c
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Original file line number Diff line number Diff line change
Expand Up @@ -46,6 +46,7 @@
#include <linux/nfs_fs.h>
#include <linux/acpi.h>
#include <linux/reboot.h>
#include <linux/ftrace.h>

#include <asm/uaccess.h>
#include <asm/processor.h>
Expand Down Expand Up @@ -455,6 +456,16 @@ static struct ctl_table kern_table[] = {
.mode = 0644,
.proc_handler = &proc_dointvec,
},
#ifdef CONFIG_FTRACE
{
.ctl_name = CTL_UNNUMBERED,
.procname = "ftrace_enabled",
.data = &ftrace_enabled,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = &ftrace_enable_sysctl,
},
#endif
#ifdef CONFIG_KMOD
{
.ctl_name = KERN_MODPROBE,
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125 changes: 107 additions & 18 deletions kernel/trace/ftrace.c
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Original file line number Diff line number Diff line change
Expand Up @@ -20,12 +20,24 @@
#include <linux/hardirq.h>
#include <linux/ftrace.h>
#include <linux/module.h>
#include <linux/sysctl.h>
#include <linux/hash.h>
#include <linux/list.h>

#include "trace.h"

#ifdef CONFIG_DYNAMIC_FTRACE
# define FTRACE_ENABLED_INIT 1
#else
# define FTRACE_ENABLED_INIT 0
#endif

int ftrace_enabled = FTRACE_ENABLED_INIT;
static int last_ftrace_enabled = FTRACE_ENABLED_INIT;

static DEFINE_SPINLOCK(ftrace_lock);
static DEFINE_MUTEX(ftrace_sysctl_lock);

static struct ftrace_ops ftrace_list_end __read_mostly =
{
.func = ftrace_stub,
Expand Down Expand Up @@ -78,14 +90,16 @@ static int notrace __register_ftrace_function(struct ftrace_ops *ops)
smp_wmb();
ftrace_list = ops;

/*
* For one func, simply call it directly.
* For more than one func, call the chain.
*/
if (ops->next == &ftrace_list_end)
ftrace_trace_function = ops->func;
else
ftrace_trace_function = ftrace_list_func;
if (ftrace_enabled) {
/*
* For one func, simply call it directly.
* For more than one func, call the chain.
*/
if (ops->next == &ftrace_list_end)
ftrace_trace_function = ops->func;
else
ftrace_trace_function = ftrace_list_func;
}

spin_unlock(&ftrace_lock);

Expand Down Expand Up @@ -120,10 +134,12 @@ static int notrace __unregister_ftrace_function(struct ftrace_ops *ops)

*p = (*p)->next;

/* If we only have one func left, then call that directly */
if (ftrace_list == &ftrace_list_end ||
ftrace_list->next == &ftrace_list_end)
ftrace_trace_function = ftrace_list->func;
if (ftrace_enabled) {
/* If we only have one func left, then call that directly */
if (ftrace_list == &ftrace_list_end ||
ftrace_list->next == &ftrace_list_end)
ftrace_trace_function = ftrace_list->func;
}

out:
spin_unlock(&ftrace_lock);
Expand Down Expand Up @@ -263,7 +279,8 @@ static void notrace ftrace_startup(void)
goto out;
__unregister_ftrace_function(&ftrace_shutdown_ops);

ftrace_run_startup_code();
if (ftrace_enabled)
ftrace_run_startup_code();
out:
mutex_unlock(&ftraced_lock);
}
Expand All @@ -275,13 +292,32 @@ static void notrace ftrace_shutdown(void)
if (ftraced_suspend)
goto out;

ftrace_run_shutdown_code();
if (ftrace_enabled)
ftrace_run_shutdown_code();

__register_ftrace_function(&ftrace_shutdown_ops);
out:
mutex_unlock(&ftraced_lock);
}

static void notrace ftrace_startup_sysctl(void)
{
mutex_lock(&ftraced_lock);
/* ftraced_suspend is true if we want ftrace running */
if (ftraced_suspend)
ftrace_run_startup_code();
mutex_unlock(&ftraced_lock);
}

static void notrace ftrace_shutdown_sysctl(void)
{
mutex_lock(&ftraced_lock);
/* ftraced_suspend is true if ftrace is running */
if (ftraced_suspend)
ftrace_run_shutdown_code();
mutex_unlock(&ftraced_lock);
}

static cycle_t ftrace_update_time;
static unsigned long ftrace_update_cnt;
unsigned long ftrace_update_tot_cnt;
Expand Down Expand Up @@ -341,8 +377,9 @@ static int notrace ftraced(void *ignore)
/* check once a second */
schedule_timeout(HZ);

mutex_lock(&ftrace_sysctl_lock);
mutex_lock(&ftraced_lock);
if (ftraced_trigger && !ftraced_suspend) {
if (ftrace_enabled && ftraced_trigger && !ftraced_suspend) {
ftrace_record_suspend++;
ftrace_update_code();
usecs = nsecs_to_usecs(ftrace_update_time);
Expand All @@ -360,6 +397,7 @@ static int notrace ftraced(void *ignore)
ftrace_record_suspend--;
}
mutex_unlock(&ftraced_lock);
mutex_unlock(&ftrace_sysctl_lock);

ftrace_shutdown_replenish();

Expand Down Expand Up @@ -389,8 +427,10 @@ static int __init notrace ftrace_shutdown_init(void)

core_initcall(ftrace_shutdown_init);
#else
# define ftrace_startup() do { } while (0)
# define ftrace_shutdown() do { } while (0)
# define ftrace_startup() do { } while (0)
# define ftrace_shutdown() do { } while (0)
# define ftrace_startup_sysctl() do { } while (0)
# define ftrace_shutdown_sysctl() do { } while (0)
#endif /* CONFIG_DYNAMIC_FTRACE */

/**
Expand All @@ -406,9 +446,15 @@ core_initcall(ftrace_shutdown_init);
*/
int register_ftrace_function(struct ftrace_ops *ops)
{
int ret;

mutex_lock(&ftrace_sysctl_lock);
ftrace_startup();

return __register_ftrace_function(ops);
ret = __register_ftrace_function(ops);
mutex_unlock(&ftrace_sysctl_lock);

return ret;
}

/**
Expand All @@ -421,10 +467,53 @@ int unregister_ftrace_function(struct ftrace_ops *ops)
{
int ret;

mutex_lock(&ftrace_sysctl_lock);
ret = __unregister_ftrace_function(ops);

if (ftrace_list == &ftrace_list_end)
ftrace_shutdown();

mutex_unlock(&ftrace_sysctl_lock);

return ret;
}

notrace int
ftrace_enable_sysctl(struct ctl_table *table, int write,
struct file *filp, void __user *buffer, size_t *lenp,
loff_t *ppos)
{
int ret;

mutex_lock(&ftrace_sysctl_lock);

ret = proc_dointvec(table, write, filp, buffer, lenp, ppos);

if (ret || !write || (last_ftrace_enabled == ftrace_enabled))
goto out;

last_ftrace_enabled = ftrace_enabled;

if (ftrace_enabled) {

ftrace_startup_sysctl();

/* we are starting ftrace again */
if (ftrace_list != &ftrace_list_end) {
if (ftrace_list->next == &ftrace_list_end)
ftrace_trace_function = ftrace_list->func;
else
ftrace_trace_function = ftrace_list_func;
}

} else {
/* stopping ftrace calls (just send to ftrace_stub) */
ftrace_trace_function = ftrace_stub;

ftrace_shutdown_sysctl();
}

out:
mutex_unlock(&ftrace_sysctl_lock);
return ret;
}

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