Re: [PATCH v7 02/10] tracing: add basic event trigger framework

[Steven Rostedt]

On Tue, 27 Aug 2013 14:40:14 -0500
Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx> wrote:

 
> Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
> Idea-by: Steve Rostedt <rostedt@xxxxxxxxxxx>
> ---
>  include/linux/ftrace_event.h        |  13 +-
>  include/trace/ftrace.h              |   4 +
>  kernel/trace/Makefile               |   1 +
>  kernel/trace/trace.h                | 171 ++++++++++++++++++++++
>  kernel/trace/trace_events.c         |  21 ++-
>  kernel/trace/trace_events_trigger.c | 280 ++++++++++++++++++++++++++++++++++++
>  kernel/trace/trace_syscalls.c       |   4 +
>  7 files changed, 488 insertions(+), 6 deletions(-)
>  create mode 100644 kernel/trace/trace_events_trigger.c
> 
> diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
> index 5eaa746..4b4fa62 100644
> --- a/include/linux/ftrace_event.h
> +++ b/include/linux/ftrace_event.h
> @@ -255,6 +255,7 @@ enum {
>  	FTRACE_EVENT_FL_RECORDED_CMD_BIT,
>  	FTRACE_EVENT_FL_SOFT_MODE_BIT,
>  	FTRACE_EVENT_FL_SOFT_DISABLED_BIT,
> +	FTRACE_EVENT_FL_TRIGGER_MODE_BIT,
>  };
>  
>  /*
> @@ -263,13 +264,15 @@ enum {
>   *  RECORDED_CMD  - The comms should be recorded at sched_switch
>   *  SOFT_MODE     - The event is enabled/disabled by SOFT_DISABLED
>   *  SOFT_DISABLED - When set, do not trace the event (even though its
> - *                   tracepoint may be enabled)
> + *                  tracepoint may be enabled)

Nitpick... I like the extra space in the indentation. It makes the
continuation of the line obvious. Otherwise I start reading the next
line as part of the original line.


> + *  TRIGGER_MODE  - The event is enabled/disabled by SOFT_DISABLED
>   */
>  enum {
>  	FTRACE_EVENT_FL_ENABLED		= (1 << FTRACE_EVENT_FL_ENABLED_BIT),
>  	FTRACE_EVENT_FL_RECORDED_CMD	= (1 << FTRACE_EVENT_FL_RECORDED_CMD_BIT),
>  	FTRACE_EVENT_FL_SOFT_MODE	= (1 << FTRACE_EVENT_FL_SOFT_MODE_BIT),
>  	FTRACE_EVENT_FL_SOFT_DISABLED	= (1 << FTRACE_EVENT_FL_SOFT_DISABLED_BIT),
> +	FTRACE_EVENT_FL_TRIGGER_MODE	= (1 << FTRACE_EVENT_FL_TRIGGER_MODE_BIT),
>  };
>  
>  struct ftrace_event_file {
> @@ -278,6 +281,7 @@ struct ftrace_event_file {
>  	struct dentry			*dir;
>  	struct trace_array		*tr;
>  	struct ftrace_subsystem_dir	*system;
> +	struct list_head		triggers;
>  
>  	/*
>  	 * 32 bit flags:
> @@ -285,6 +289,7 @@ struct ftrace_event_file {
>  	 *   bit 1:		enabled cmd record
>  	 *   bit 2:		enable/disable with the soft disable bit
>  	 *   bit 3:		soft disabled
> +	 *   bit 4:		trigger enabled
>  	 *
>  	 * Note: The bits must be set atomically to prevent races
>  	 * from other writers. Reads of flags do not need to be in
> @@ -296,6 +301,7 @@ struct ftrace_event_file {
>  	 */
>  	unsigned long		flags;
>  	atomic_t		sm_ref;	/* soft-mode reference counter */
> +	atomic_t		tm_ref;	/* trigger-mode reference counter */
>  };
>  
>  #define __TRACE_EVENT_FLAGS(name, value)				\
> @@ -310,12 +316,17 @@ struct ftrace_event_file {
>  
>  #define MAX_FILTER_STR_VAL	256	/* Should handle KSYM_SYMBOL_LEN */
>  
> +enum event_trigger_type {
> +	ETT_NONE		= (0),
> +};
> +
>  extern void destroy_preds(struct ftrace_event_call *call);
>  extern int filter_match_preds(struct event_filter *filter, void *rec);
>  extern int filter_current_check_discard(struct ring_buffer *buffer,
>  					struct ftrace_event_call *call,
>  					void *rec,
>  					struct ring_buffer_event *event);
> +extern void event_triggers_call(struct ftrace_event_file *file);
>  
>  enum {
>  	FILTER_OTHER = 0,
> diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
> index 41a6643..326ba32 100644
> --- a/include/trace/ftrace.h
> +++ b/include/trace/ftrace.h
> @@ -526,6 +526,10 @@ ftrace_raw_event_##call(void *__data, proto)				\
>  	int __data_size;						\
>  	int pc;								\
>  									\
> +	if (test_bit(FTRACE_EVENT_FL_TRIGGER_MODE_BIT,			\
> +		     &ftrace_file->flags))				\
> +		event_triggers_call(ftrace_file);			\
> +									\
>  	if (test_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT,			\
>  		     &ftrace_file->flags))				\
>  		return;							\
> diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
> index d7e2068..1378e84 100644
> --- a/kernel/trace/Makefile
> +++ b/kernel/trace/Makefile
> @@ -50,6 +50,7 @@ ifeq ($(CONFIG_PERF_EVENTS),y)
>  obj-$(CONFIG_EVENT_TRACING) += trace_event_perf.o
>  endif
>  obj-$(CONFIG_EVENT_TRACING) += trace_events_filter.o
> +obj-$(CONFIG_EVENT_TRACING) += trace_events_trigger.o
>  obj-$(CONFIG_KPROBE_EVENT) += trace_kprobe.o
>  obj-$(CONFIG_TRACEPOINTS) += power-traces.o
>  ifeq ($(CONFIG_PM_RUNTIME),y)
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index b1227b9..f8a18e5 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -1016,9 +1016,180 @@ extern void trace_event_enable_cmd_record(bool enable);
>  extern int event_trace_add_tracer(struct dentry *parent, struct trace_array *tr);
>  extern int event_trace_del_tracer(struct trace_array *tr);
>  
> +static inline void *event_file_data(struct file *filp)
> +{
> +	return ACCESS_ONCE(file_inode(filp)->i_private);
> +}
> +
>  extern struct mutex event_mutex;
>  extern struct list_head ftrace_events;
>  
> +extern const struct file_operations event_trigger_fops;
> +
> +extern int register_trigger_cmds(void);
> +extern void clear_event_triggers(struct trace_array *tr);
> +
> +/**
> + * struct event_trigger_ops - callbacks for trace event triggers
> + *
> + * The methods in this structure provide per-event trigger hooks for
> + * various trigger operations.
> + *
> + * All the methods below, except for @init() and @free(), must be
> + * implemented.
> + *
> + * @func: The trigger 'probe' function called when the triggering
> + *	event occurs.  The data passed into this callback is the data
> + *	that was supplied to the event_command @reg() function that
> + *	registered the trigger (see struct event_command).
> + *
> + * @init: An optional initialization function called for the trigger
> + *	when the trigger is registered (via the event_command reg()
> + *	function).  This can be used to perform per-trigger
> + *	initialization such as incrementing a per-trigger reference
> + *	count, for instance.  This is usually implemented by the
> + *	generic utility function @event_trigger_init() (see
> + *	trace_event_triggers.c).
> + *
> + * @free: An optional de-initialization function called for the
> + *	trigger when the trigger is unregistered (via the
> + *	event_command @reg() function).  This can be used to perform
> + *	per-trigger de-initialization such as decrementing a
> + *	per-trigger reference count and freeing corresponding trigger
> + *	data, for instance.  This is usually implemented by the
> + *	generic utility function @event_trigger_free() (see
> + *	trace_event_triggers.c).
> + *
> + * @print: The callback function invoked to have the trigger print
> + *	itself.  This is usually implemented by a wrapper function
> + *	that calls the generic utility function @event_trigger_print()
> + *	(see trace_event_triggers.c).
> + */
> +struct event_trigger_ops {
> +	void			(*func)(void **data);

Why the void **?

> +	int			(*init)(struct event_trigger_ops *ops,
> +					void **data);
> +	void			(*free)(struct event_trigger_ops *ops,
> +					void **data);
> +	int			(*print)(struct seq_file *m,
> +					 struct event_trigger_ops *ops,
> +					 void *data);
> +};
> +
> +/**
> + * struct event_command - callbacks and data members for event commands
> + *
> + * Event commands are invoked by users by writing the command name
> + * into the 'trigger' file associated with a trace event.  The
> + * parameters associated with a specific invocation of an event
> + * command are used to create an event trigger instance, which is
> + * added to the list of trigger instances associated with that trace
> + * event.  When the event is hit, the set of triggers associated with
> + * that event is invoked.
> + *
> + * The data members in this structure provide per-event command data
> + * for various event commands.
> + *
> + * All the data members below, except for @post_trigger, must be set
> + * for each event command.
> + *
> + * @name: The unique name that identifies the event command.  This is
> + *	the name used when setting triggers via trigger files.
> + *
> + * @trigger_type: A unique id that identifies the event command
> + *	'type'.  This value has two purposes, the first to ensure that
> + *	only one trigger of the same type can be set at a given time
> + *	for a particular event e.g. it doesn't make sense to have both
> + *	a traceon and traceoff trigger attached to a single event at
> + *	the same time, so traceon and traceoff have the same type
> + *	though they have different names.  The @trigger_type value is

Heh, I didn't bother for that in the ftrace triggers. If the root user
wants to start and stop tracing on the same function, so be it. They
get what they ask for.

I'm not against this, I was just pointing out how you care more than I
do about keeping root from stepping on his/her own toes ;-)

> + *	also used as a bit value for deferring the actual trigger
> + *	action until after the current event is finished.  Some
> + *	commands need to do this if they themselves log to the trace
> + *	buffer (see the @post_trigger() member below).  @trigger_type
> + *	values are defined by adding new values to the trigger_type
> + *	enum in include/linux/ftrace_event.h.
> + *
> + * @post_trigger: A flag that says whether or not this command needs
> + *	to have its action delayed until after the current event has
> + *	been closed.  Some triggers need to avoid being invoked while
> + *	an event is currently in the process of being logged, since
> + *	the trigger may itself log data into the trace buffer.  Thus
> + *	we make sure the current event is committed before invoking
> + *	those triggers.  To do that, the trigger invocation is split
> + *	in two - the first part checks the filter using the current
> + *	trace record; if a command has the @post_trigger flag set, it
> + *	sets a bit for itself in the return value, otherwise it
> + *	directly invokes the trigger.  Once all commands have been
> + *	either invoked or set their return flag, the current record is
> + *	either committed or discarded.  At that point, if any commands
> + *	have deferred their triggers, those commands are finally
> + *	invoked following the close of the current event.  In other
> + *	words, if the event_trigger_ops @func() probe implementation
> + *	itself logs to the trace buffer, this flag should be set,
> + *	otherwise it can be left unspecified.

Is this just for consistency of output layout? So the normal event gets
printed first before this prints anything, like a stack trace?

> + *
> + * All the methods below, except for @set_filter(), must be
> + * implemented.
> + *
> + * @func: The callback function responsible for parsing and
> + *	registering the trigger written to the 'trigger' file by the
> + *	user.  It allocates the trigger instance and registers it with
> + *	the appropriate trace event.  It makes use of the other
> + *	event_command callback functions to orchestrate this, and is
> + *	usually implemented by the generic utility function
> + *	@event_trigger_callback() (see trace_event_triggers.c).
> + *
> + * @reg: Adds the trigger to the list of triggers associated with the
> + *	event, and enables the event trigger itself, after
> + *	initializing it (via the event_trigger_ops @init() function).
> + *	This is also where commands can use the @trigger_type value to
> + *	make the decision as to whether or not multiple instances of
> + *	the trigger should be allowed.  This is usually implemented by
> + *	the generic utility function @register_trigger() (see
> + *	trace_event_triggers.c).
> + *
> + * @unreg: Removes the trigger from the list of triggers associated
> + *	with the event, and disables the event trigger itself, after
> + *	initializing it (via the event_trigger_ops @free() function).
> + *	This is usually implemented by the generic utility function
> + *	@unregister_trigger() (see trace_event_triggers.c).
> + *
> + * @set_filter: An optional function called to parse and set a filter
> + *	for the trigger.  If no @set_filter() method is set for the
> + *	event command, filters set by the user for the command will be
> + *	ignored.  This is usually implemented by the generic utility
> + *	function @set_trigger_filter() (see trace_event_triggers.c).
> + *
> + * @get_trigger_ops: The callback function invoked to retrieve the
> + *	event_trigger_ops implementation associated with the command.
> + */
> +struct event_command {
> +	struct list_head	list;
> +	char			*name;
> +	enum event_trigger_type	trigger_type;
> +	bool			post_trigger;
> +	int			(*func)(struct event_command *cmd_ops,
> +					struct ftrace_event_file *file,
> +					char *glob, char *cmd,
> +					char *params, int enable);
> +	int			(*reg)(char *glob,
> +				       struct event_trigger_ops *trigger_ops,
> +				       void *trigger_data,
> +				       struct ftrace_event_file *file);
> +	void			(*unreg)(char *glob,
> +					 struct event_trigger_ops *trigger_ops,
> +					 void *trigger_data,
> +					 struct ftrace_event_file *file);
> +	int			(*set_filter)(char *filter_str,
> +					      void *trigger_data,
> +					      struct ftrace_event_file *file);
> +	struct event_trigger_ops *(*get_trigger_ops)(char *cmd, char *param);
> +};
> +
> +extern int trace_event_enable_disable(struct ftrace_event_file *file,
> +				      int enable, int soft_disable);
> +
>  extern const char *__start___trace_bprintk_fmt[];
>  extern const char *__stop___trace_bprintk_fmt[];
>  
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 368a4d5..7d8eb8a 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -342,6 +342,12 @@ static int __ftrace_event_enable_disable(struct ftrace_event_file *file,
>  	return ret;
>  }
>  
> +int trace_event_enable_disable(struct ftrace_event_file *file,
> +			       int enable, int soft_disable)
> +{
> +	return __ftrace_event_enable_disable(file, enable, soft_disable);
> +}
> +
>  static int ftrace_event_enable_disable(struct ftrace_event_file *file,
>  				       int enable)
>  {
> @@ -421,11 +427,6 @@ static void remove_subsystem(struct ftrace_subsystem_dir *dir)
>  	}
>  }
>  
> -static void *event_file_data(struct file *filp)
> -{
> -	return ACCESS_ONCE(file_inode(filp)->i_private);
> -}
> -
>  static void remove_event_file_dir(struct ftrace_event_file *file)
>  {
>  	struct dentry *dir = file->dir;
> @@ -1542,6 +1543,9 @@ event_create_dir(struct dentry *parent, struct ftrace_event_file *file)
>  	trace_create_file("filter", 0644, file->dir, call,
>  			  &ftrace_event_filter_fops);
>  
> +	trace_create_file("trigger", 0644, file->dir, file,
> +			  &event_trigger_fops);
> +
>  	trace_create_file("format", 0444, file->dir, call,
>  			  &ftrace_event_format_fops);
>  
> @@ -1637,6 +1641,8 @@ trace_create_new_event(struct ftrace_event_call *call,
>  	file->event_call = call;
>  	file->tr = tr;
>  	atomic_set(&file->sm_ref, 0);
> +	atomic_set(&file->tm_ref, 0);
> +	INIT_LIST_HEAD(&file->triggers);
>  	list_add(&file->list, &tr->events);
>  
>  	return file;
> @@ -2303,6 +2309,9 @@ int event_trace_del_tracer(struct trace_array *tr)
>  {
>  	mutex_lock(&event_mutex);
>  
> +	/* Disable any event triggers and associated soft-disabled events */
> +	clear_event_triggers(tr);
> +
>  	/* Disable any running events */
>  	__ftrace_set_clr_event_nolock(tr, NULL, NULL, NULL, 0);
>  
> @@ -2366,6 +2375,8 @@ static __init int event_trace_enable(void)
>  
>  	register_event_cmds();
>  
> +	register_trigger_cmds();
> +
>  	return 0;
>  }
>  
> diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
> new file mode 100644
> index 0000000..5ec8336
> --- /dev/null
> +++ b/kernel/trace/trace_events_trigger.c
> @@ -0,0 +1,280 @@
> +/*
> + * trace_events_trigger - trace event triggers
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software
> + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
> + *
> + * Copyright (C) 2013 Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
> + */
> +
> +#include <linux/module.h>
> +#include <linux/ctype.h>
> +#include <linux/mutex.h>
> +#include <linux/slab.h>
> +
> +#include "trace.h"
> +
> +static LIST_HEAD(trigger_commands);
> +static DEFINE_MUTEX(trigger_cmd_mutex);
> +
> +struct event_trigger_data {
> +	struct ftrace_event_file	*file;
> +	unsigned long			count;
> +	int				ref;
> +	bool				enable;
> +	struct event_trigger_ops	*ops;
> +	struct event_command *		cmd_ops;
> +	struct event_filter		*filter;
> +	char				*filter_str;
> +	struct list_head		list;
> +};
> +
> +void event_triggers_call(struct ftrace_event_file *file)
> +{
> +	struct event_trigger_data *data;
> +
> +	if (list_empty(&file->triggers))
> +		return;
> +
> +	preempt_disable_notrace();
> +	list_for_each_entry_rcu(data, &file->triggers, list)
> +		data->ops->func((void **)&data);

Why is this a void ** and why are you passing the address of the
variable that holds the pointer to the data that was registered and not
the pointer to the data itself?

Do you plan on modifying the local data variable on return?

> +	preempt_enable_notrace();
> +}
> +EXPORT_SYMBOL_GPL(event_triggers_call);
> +
> +static void *trigger_next(struct seq_file *m, void *t, loff_t *pos)
> +{
> +	struct ftrace_event_file *event_file = event_file_data(m->private);
> +
> +	return seq_list_next(t, &event_file->triggers, pos);
> +}
> +
> +static void *trigger_start(struct seq_file *m, loff_t *pos)
> +{
> +	struct ftrace_event_file *event_file;
> +
> +	/* ->stop() is called even if ->start() fails */
> +	mutex_lock(&event_mutex);
> +	event_file = event_file_data(m->private);
> +	if (unlikely(!event_file))
> +		return ERR_PTR(-ENODEV);
> +
> +	return seq_list_start(&event_file->triggers, *pos);
> +}
> +
> +static void trigger_stop(struct seq_file *m, void *t)
> +{
> +	mutex_unlock(&event_mutex);
> +}
> +
> +static int trigger_show(struct seq_file *m, void *v)
> +{
> +	struct event_trigger_data *data;
> +
> +	data = list_entry(v, struct event_trigger_data, list);
> +	data->ops->print(m, data->ops, data);
> +
> +	return 0;
> +}
> +
> +static const struct seq_operations event_triggers_seq_ops = {
> +	.start = trigger_start,
> +	.next = trigger_next,
> +	.stop = trigger_stop,
> +	.show = trigger_show,
> +};
> +
> +static int event_trigger_regex_open(struct inode *inode, struct file *file)
> +{
> +	int ret = 0;
> +
> +	mutex_lock(&event_mutex);
> +
> +	if (unlikely(!event_file_data(file))) {
> +		mutex_unlock(&event_mutex);
> +		return -ENODEV;
> +	}
> +
> +	if (file->f_mode & FMODE_READ) {
> +		ret = seq_open(file, &event_triggers_seq_ops);
> +		if (!ret) {
> +			struct seq_file *m = file->private_data;
> +			m->private = file;
> +		}
> +	}
> +
> +	mutex_unlock(&event_mutex);
> +
> +	return ret;
> +}
> +
> +static int trigger_process_regex(struct ftrace_event_file *file,
> +				 char *buff, int enable)
> +{
> +	char *command, *next = buff;
> +	struct event_command *p;
> +	int ret = -EINVAL;
> +
> +	command = strsep(&next, ": \t");
> +	command = (command[0] != '!') ? command : command + 1;
> +
> +	mutex_lock(&trigger_cmd_mutex);
> +	list_for_each_entry(p, &trigger_commands, list) {
> +		if (strcmp(p->name, command) == 0) {
> +			ret = p->func(p, file, buff, command, next, enable);
> +			goto out_unlock;
> +		}
> +	}
> + out_unlock:
> +	mutex_unlock(&trigger_cmd_mutex);
> +
> +	return ret;
> +}
> +
> +static ssize_t event_trigger_regex_write(struct file *file,
> +					 const char __user *ubuf,
> +					 size_t cnt, loff_t *ppos, int enable)
> +{
> +	struct ftrace_event_file *event_file;
> +	ssize_t ret;
> +	char *buf;
> +
> +	if (!cnt)
> +		return 0;
> +
> +	if (cnt >= PAGE_SIZE)
> +		return -EINVAL;
> +
> +	buf = (char *)__get_free_page(GFP_TEMPORARY);
> +	if (!buf)
> +		return -ENOMEM;
> +
> +	if (copy_from_user(buf, ubuf, cnt)) {
> +		free_page((unsigned long) buf);
> +		return -EFAULT;
> +	}
> +	buf[cnt] = '\0';
> +	strim(buf);
> +
> +	mutex_lock(&event_mutex);
> +	event_file = event_file_data(file);
> +	if (unlikely(!event_file)) {
> +		mutex_unlock(&event_mutex);
> +		free_page((unsigned long) buf);
> +		return -ENODEV;
> +	}
> +	ret = trigger_process_regex(event_file, buf, enable);
> +	mutex_unlock(&event_mutex);
> +
> +	free_page((unsigned long) buf);
> +	if (ret < 0)
> +		goto out;
> +
> +	*ppos += cnt;
> +	ret = cnt;
> + out:
> +	return ret;
> +}
> +
> +static int event_trigger_regex_release(struct inode *inode, struct file *file)
> +{
> +	mutex_lock(&event_mutex);
> +
> +	if (file->f_mode & FMODE_READ)
> +		seq_release(inode, file);
> +
> +	mutex_unlock(&event_mutex);
> +
> +	return 0;
> +}
> +
> +static ssize_t
> +event_trigger_write(struct file *filp, const char __user *ubuf,
> +		    size_t cnt, loff_t *ppos)
> +{
> +	return event_trigger_regex_write(filp, ubuf, cnt, ppos, 1);
> +}
> +
> +static int
> +event_trigger_open(struct inode *inode, struct file *filp)
> +{
> +	return event_trigger_regex_open(inode, filp);
> +}
> +
> +static int
> +event_trigger_release(struct inode *inode, struct file *file)
> +{
> +	return event_trigger_regex_release(inode, file);
> +}
> +
> +const struct file_operations event_trigger_fops = {
> +	.open = event_trigger_open,
> +	.read = seq_read,
> +	.write = event_trigger_write,
> +	.llseek = ftrace_filter_lseek,
> +	.release = event_trigger_release,
> +};
> +
> +static int trace_event_trigger_enable_disable(struct ftrace_event_file *file,
> +					      int trigger_enable)
> +{
> +	int ret = 0;
> +
> +	if (trigger_enable) {
> +		if (atomic_inc_return(&file->tm_ref) > 1)
> +			return ret;
> +		set_bit(FTRACE_EVENT_FL_TRIGGER_MODE_BIT, &file->flags);
> +		ret = trace_event_enable_disable(file, 1, 1);
> +	} else {
> +		if (atomic_dec_return(&file->tm_ref) > 0)
> +			return ret;
> +		clear_bit(FTRACE_EVENT_FL_TRIGGER_MODE_BIT, &file->flags);
> +		ret = trace_event_enable_disable(file, 0, 1);
> +	}
> +
> +	return ret;
> +}
> +
> +/**
> + * clear_event_triggers - clear all triggers associated with a trace array.
> + *
> + * For each trigger, the triggering event has its tm_ref decremented
> + * via trace_event_trigger_enable_disable(), and any associated event
> + * (in the case of enable/disable_event triggers) will have its sm_ref
> + * decremented via free()->trace_event_enable_disable().  That
> + * combination effectively reverses the soft-mode/trigger state added
> + * by trigger registration.
> + *
> + * Must be called with event_mutex held.
> + */
> +void
> +clear_event_triggers(struct trace_array *tr)
> +{
> +	struct ftrace_event_file *file;
> +
> +	list_for_each_entry(file, &tr->events, list) {
> +		struct event_trigger_data *data;
> +		list_for_each_entry_rcu(data, &file->triggers, list) {
> +			trace_event_trigger_enable_disable(file, 0);
> +			if (data->ops->free)
> +				data->ops->free(data->ops, (void **)&data);

ditto here.

-- Steve

> +		}
> +	}
> +}
> +
> +__init int register_trigger_cmds(void)
> +{
> +	return 0;
> +}
> diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
> index 230cdb6..4f56d54 100644
> --- a/kernel/trace/trace_syscalls.c
> +++ b/kernel/trace/trace_syscalls.c
> @@ -321,6 +321,8 @@ static void ftrace_syscall_enter(void *data, struct pt_regs *regs, long id)
>  	if (!ftrace_file)
>  		return;
>  
> +	if (test_bit(FTRACE_EVENT_FL_TRIGGER_MODE_BIT, &ftrace_file->flags))
> +		event_triggers_call(ftrace_file);
>  	if (test_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT, &ftrace_file->flags))
>  		return;
>  
> @@ -370,6 +372,8 @@ static void ftrace_syscall_exit(void *data, struct pt_regs *regs, long ret)
>  	if (!ftrace_file)
>  		return;
>  
> +	if (test_bit(FTRACE_EVENT_FL_TRIGGER_MODE_BIT, &ftrace_file->flags))
> +		event_triggers_call(ftrace_file);
>  	if (test_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT, &ftrace_file->flags))
>  		return;
>  

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