by Tom Zanussi

[permalink] [raw]

Subject: Re: [PATCH v4 0/7] tracing: 'hist' triggers

On Tue, 2015-04-21 at 12:36 +0200, Daniel Wagner wrote:
> Hi Tom,
>
> On 04/21/2015 12:03 AM, Tom Zanussi wrote:
> > On Mon, 2015-04-20 at 14:52 +0200, Daniel Wagner wrote:
> >> On 04/10/2015 06:05 PM, Tom Zanussi wrote:
> >> So I am wondering if the path from ftrace_trigger_soft_disabled()
> >> to event_triggers_call() is supposed never to happen? The comment
> >> on ftrace_trigger_soft_disabled() indicate this might happen on
> >> normal operation:
> >>
> >
> > So I looked at this on the plane and you're right, this is a path that
> > should never be taken in this case, since the hist trigger does set the
> > post_trigger flag and should therefore TRIGGER_COND would be true and
> > that block should never be entered.
> >
> > However, the code that registers the trigger first enables the event,
> > then sets the cond flag, which would allow this to happen - a trigger
> > expecting data would be passed a NULL rec.
> >
> > Can you try the patch below and see if it fixes the problem? (untested
> > and I haven't even had a chance to compile-test it..)
>
> Thanks for the explanation. With that and your patch I could get
> it working. There are a couple of calling places missing in your
> patch. With them it works nicely. Maybe moving update_cond_flag()
> inside trace_event_trigger_enable_disable() would be an option?
>

Yeah, I guess I missed the most important bit in my haste, but glad it
works for you now. I'll write up a proper patch as soon as I can..

Thanks,

Tom

> cheers,
> daniel
>
>
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 4d8f5df..221ab1f 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -1471,11 +1471,12 @@ static int hist_register_trigger(char *glob, struct event_trigger_ops *ops,
> list_add_rcu(&data->list, &file->triggers);
> ret++;
>
> + update_cond_flag(file);
> if (trace_event_trigger_enable_disable(file, 1) < 0) {
> list_del_rcu(&data->list);
> + update_cond_flag(file);
> ret--;
> }
> - update_cond_flag(file);
> out:
> return ret;
> }
> diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
> index 8c8f2ee..e47a229 100644
> --- a/kernel/trace/trace_events_trigger.c
> +++ b/kernel/trace/trace_events_trigger.c
> @@ -1264,6 +1264,7 @@ int event_enable_trigger_func(struct event_command *cmd_ops,
> goto out_free;
> }
>
> + update_cond_flag(file);
> ret = trace_event_enable_disable(event_enable_file, 1, 1);
> if (ret < 0)
> goto out_put;
> @@ -1286,6 +1287,7 @@ int event_enable_trigger_func(struct event_command *cmd_ops,
> out_disable:
> trace_event_enable_disable(event_enable_file, 0, 1);
> out_put:
> + update_cond_flag(file);
> module_put(event_enable_file->event_call->mod);
> out_free:
> if (cmd_ops->set_filter)
>
>
>
>
> > Tom
> >
> > [PATCH] tracing: Update cond flag before enabling or disabling a trigger
> >
> > Before a trigger is enabled, the cond flag should be set beforehand,
> > otherwise an trigger that's expecting to process a trace record
> > (e.g. one with post_trigger set) could be invoked without one.
> >
> > Likewise a trigger's cond flag should be reset after it's disabled,
> > not before.
> >
> > Signed-off-by: Tom Zanussi <[email protected]>
> > ---
> > kernel/trace/trace_events_trigger.c | 10 ++++++----
> > 1 file changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
> > index 7105f15..108e46c 100644
> > --- a/kernel/trace/trace_events_trigger.c
> > +++ b/kernel/trace/trace_events_trigger.c
> > @@ -546,11 +546,12 @@ static int register_trigger(char *glob, struct event_trigger_ops *ops,
> > list_add_rcu(&data->list, &file->triggers);
> > ret++;
> >
> > + update_cond_flag(file);
> > if (trace_event_trigger_enable_disable(file, 1) < 0) {
> > list_del_rcu(&data->list);
> > + update_cond_flag(file);
> > ret--;
> > }
> > - update_cond_flag(file);
> > out:
> > return ret;
> > }
> > @@ -578,8 +579,8 @@ void unregister_trigger(char *glob, struct event_trigger_ops *ops,
> > if (data->cmd_ops->trigger_type == test->cmd_ops->trigger_type) {
> > unregistered = true;
> > list_del_rcu(&data->list);
> > - update_cond_flag(file);
> > trace_event_trigger_enable_disable(file, 0);
> > + update_cond_flag(file);
> > break;
> > }
> > }
> > @@ -1324,11 +1325,12 @@ int event_enable_register_trigger(char *glob,
> > list_add_rcu(&data->list, &file->triggers);
> > ret++;
> >
> > + update_cond_flag(file);
> > if (trace_event_trigger_enable_disable(file, 1) < 0) {
> > list_del_rcu(&data->list);
> > + update_cond_flag(file);
> > ret--;
> > }
> > - update_cond_flag(file);
> > out:
> > return ret;
> > }
> > @@ -1351,8 +1353,8 @@ void event_enable_unregister_trigger(char *glob,
> > (enable_data->file == test_enable_data->file)) {
> > unregistered = true;
> > list_del_rcu(&data->list);
> > - update_cond_flag(file);
> > trace_event_trigger_enable_disable(file, 0);
> > + update_cond_flag(file);
> > break;
> > }
> > }
> >