Re: [PATCH 4/4] tracing/events: fix concurrent access to ftrace_events list

Frederic Weisbecker
2009-05-06T05:27:45Z

On Wed, May 06, 2009 at 10:33:45AM +0800, Li Zefan wrote:
> 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: Li Zefan <lizf@cn.fujitsu.com>

Nice series of fixes!

Thanks!

Frederic.

> ---
> kernel/trace/trace.h | 1 +
> kernel/trace/trace_event_profile.c | 19 ++++++++++++++-----
> kernel/trace/trace_events.c | 20 +++++++++++---------
> kernel/trace/trace_events_filter.c | 10 +++++++---
> 4 files changed, 33 insertions(+), 17 deletions(-)
>
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 83984ab..0bba080 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -827,6 +827,7 @@ 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[];
> diff --git a/kernel/trace/trace_event_profile.c b/kernel/trace/trace_event_profile.c
> index 7bf2ad6..5b5895a 100644
> --- a/kernel/trace/trace_event_profile.c
> +++ b/kernel/trace/trace_event_profile.c
> @@ -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);
> }
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 72d619d..ac5b1c2 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -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
> diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
> index 97bd140..8c62e5b 100644
> --- a/kernel/trace/trace_events_filter.c
> +++ b/kernel/trace/trace_events_filter.c
> @@ -433,6 +433,7 @@ 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;
> @@ -442,6 +443,7 @@ 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,
> @@ -605,6 +607,7 @@ 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),
> @@ -622,8 +625,8 @@ 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;
> @@ -635,12 +638,13 @@ 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,
> --
> 1.5.4.rc3
>
>