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SubjectRe: [PATCH v4 0/7] tracing: 'hist' triggers
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?

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 <tom.zanussi@linux.intel.com>
> ---
> 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;
> }
> }
>


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