Commit 20c8928a authored by Li Zefan's avatar Li Zefan Committed by Ingo Molnar
Browse files

tracing/events: fix concurrent access to ftrace_events list 



A module will add/remove its trace events when it gets loaded/unloaded, so
the ftrace_events list is not "const", and concurrent access needs to be
protected.

This patch thus fixes races between loading/unloding modules and read
'available_events' or read/write 'set_event', etc.

Below shows how to reproduce the race:

 # for ((; ;)) { cat /mnt/tracing/available_events; } > /dev/null &
 # for ((; ;)) { insmod trace-events-sample.ko; rmmod sample; } &

After a while:

BUG: unable to handle kernel paging request at 0010011c
IP: [<c1080f27>] t_next+0x1b/0x2d
...
Call Trace:
 [<c10c90e6>] ? seq_read+0x217/0x30d
 [<c10c8ecf>] ? seq_read+0x0/0x30d
 [<c10b4c19>] ? vfs_read+0x8f/0x136
 [<c10b4fc3>] ? sys_read+0x40/0x65
 [<c1002a68>] ? sysenter_do_call+0x12/0x36

[ Impact: fix races when concurrent accessing ftrace_events list ]

Signed-off-by: default avatarLi Zefan <lizf@cn.fujitsu.com>
Acked-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Acked-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <4A00F709.3080800@cn.fujitsu.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 2df75e41

kernel/trace/trace.h

+1 −0
Original line number Diff line number Diff line
@@ -825,6 +825,7 @@ static int filter_pred_##size(struct filter_pred *pred, void *event, \ 
	return match;							\

}



extern struct mutex event_mutex;

extern struct list_head ftrace_events;



extern const char *__start___trace_bprintk_fmt[];

kernel/trace/trace_event_profile.c

+14 −5
Original line number Diff line number Diff line
@@ -10,21 +10,30 @@ 
int ftrace_profile_enable(int event_id)

{

	struct ftrace_event_call *event;

	int ret = -EINVAL;



	mutex_lock(&event_mutex);

	list_for_each_entry(event, &ftrace_events, list) {

		if (event->id == event_id)

			return event->profile_enable(event);

		if (event->id == event_id) {

			ret = event->profile_enable(event);

			break;

		}

	}

	mutex_unlock(&event_mutex);



	return -EINVAL;

	return ret;

}



void ftrace_profile_disable(int event_id)

{

	struct ftrace_event_call *event;



	mutex_lock(&event_mutex);

	list_for_each_entry(event, &ftrace_events, list) {

		if (event->id == event_id)

			return event->profile_disable(event);

		if (event->id == event_id) {

			event->profile_disable(event);

			break;

		}

	}

	mutex_unlock(&event_mutex);

}

kernel/trace/trace_events.c

+11 −9
Original line number Diff line number Diff line
@@ -21,7 +21,7 @@ 


#define TRACE_SYSTEM "TRACE_SYSTEM"



static DEFINE_MUTEX(event_mutex);

DEFINE_MUTEX(event_mutex);



LIST_HEAD(ftrace_events);
@@ -80,6 +80,7 @@ static void ftrace_clear_events(void) 
{

	struct ftrace_event_call *call;



	mutex_lock(&event_mutex);

	list_for_each_entry(call, &ftrace_events, list) {



		if (call->enabled) {
@@ -87,6 +88,7 @@ static void ftrace_clear_events(void) 
			call->unregfunc();

		}

	}

	mutex_unlock(&event_mutex);

}



static void ftrace_event_enable_disable(struct ftrace_event_call *call,
@@ -274,6 +276,9 @@ t_next(struct seq_file *m, void *v, loff_t *pos) 


static void *t_start(struct seq_file *m, loff_t *pos)

{

	mutex_lock(&event_mutex);

	if (*pos == 0)

		m->private = ftrace_events.next;

	return t_next(m, NULL, pos);

}
@@ -303,6 +308,9 @@ s_next(struct seq_file *m, void *v, loff_t *pos) 


static void *s_start(struct seq_file *m, loff_t *pos)

{

	mutex_lock(&event_mutex);

	if (*pos == 0)

		m->private = ftrace_events.next;

	return s_next(m, NULL, pos);

}
@@ -319,12 +327,12 @@ static int t_show(struct seq_file *m, void *v) 


static void t_stop(struct seq_file *m, void *p)

{

	mutex_unlock(&event_mutex);

}



static int

ftrace_event_seq_open(struct inode *inode, struct file *file)

{

	int ret;

	const struct seq_operations *seq_ops;



	if ((file->f_mode & FMODE_WRITE) &&
@@ -332,13 +340,7 @@ ftrace_event_seq_open(struct inode *inode, struct file *file) 
		ftrace_clear_events();



	seq_ops = inode->i_private;

	ret = seq_open(file, seq_ops);

	if (!ret) {

		struct seq_file *m = file->private_data;



		m->private = ftrace_events.next;

	}

	return ret;

	return seq_open(file, seq_ops);

}



static ssize_t

kernel/trace/trace_events_filter.c

+7 −3
Original line number Diff line number Diff line
@@ -408,6 +408,7 @@ static void filter_free_subsystem_preds(struct event_subsystem *system) 
		filter->n_preds = 0;

	}



	mutex_lock(&event_mutex);

	list_for_each_entry(call, &ftrace_events, list) {

		if (!call->define_fields)

			continue;
@@ -417,6 +418,7 @@ static void filter_free_subsystem_preds(struct event_subsystem *system) 
			remove_filter_string(call->filter);

		}

	}

	mutex_unlock(&event_mutex);

}



static int filter_add_pred_fn(struct filter_parse_state *ps,
@@ -567,6 +569,7 @@ static int filter_add_subsystem_pred(struct filter_parse_state *ps, 
{

	struct event_filter *filter = system->filter;

	struct ftrace_event_call *call;

	int err = 0;



	if (!filter->preds) {

		filter->preds = kzalloc(MAX_FILTER_PRED * sizeof(pred),
@@ -584,8 +587,8 @@ static int filter_add_subsystem_pred(struct filter_parse_state *ps, 
	filter->preds[filter->n_preds] = pred;

	filter->n_preds++;



	mutex_lock(&event_mutex);

	list_for_each_entry(call, &ftrace_events, list) {

		int err;



		if (!call->define_fields)

			continue;
@@ -597,12 +600,13 @@ static int filter_add_subsystem_pred(struct filter_parse_state *ps, 
		if (err) {

			filter_free_subsystem_preds(system);

			parse_error(ps, FILT_ERR_BAD_SUBSYS_FILTER, 0);

			return err;

			break;

		}

		replace_filter_string(call->filter, filter_string);

	}

	mutex_unlock(&event_mutex);



	return 0;

	return err;

}



static void parse_init(struct filter_parse_state *ps,

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