Re: [PATCH v2] tracing: Restore synchronize_rcu() before freeing trigger private data

[Steven Rostedt]

On Thu, 23 Jul 2026 18:02:12 +0100
David Carlier <devnexen@xxxxxxxxx> wrote:

> ---
>  kernel/trace/trace_events_hist.c    | 3 +++
>  kernel/trace/trace_events_trigger.c | 1 +
>  2 files changed, 4 insertions(+)
> 
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 82ce492ab268..ddd2f70dac4f 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -6349,6 +6349,8 @@ static void event_hist_trigger_free(struct event_trigger_data *data)
>  
>  		trigger_data_free(data);
>  
> +		synchronize_rcu();

According to Sashiko[1], it appears we actually need tracepoint_synchronize_unregister().
And I believe Sashiko is actually correct.

> +
>  		remove_hist_vars(hist_data);
>  
>  		unregister_field_var_hists(hist_data);
> @@ -6388,6 +6390,7 @@ static void event_hist_trigger_named_free(struct
> event_trigger_data *data) 
>  		del_named_trigger(data);
>  		trigger_data_free(data);
> +		synchronize_rcu();

This needs to be changed too.

>  		kfree(cmd_ops);
>  	}
>  }
> diff --git a/kernel/trace/trace_events_trigger.c
> b/kernel/trace/trace_events_trigger.c index 655db2e82513..c3f54f2540b6
> 100644 --- a/kernel/trace/trace_events_trigger.c
> +++ b/kernel/trace/trace_events_trigger.c
> @@ -1730,6 +1730,7 @@ void event_enable_trigger_free(struct
> event_trigger_data *data) trace_event_enable_disable(enable_data->file,
> 0, 1); trace_event_put_ref(enable_data->file->event_call);
>  		trigger_data_free(data);
> +		synchronize_rcu();

According to Sashiko, this one basically causes a revert of the original
delay. 

OK, let's bring back a partial part of your original patch. Have the
"free_private()" again, but only apply it to this trigger, and switch the
above other to synchronize_rcu() into the tracepoint_synchronize_unregister().

Thanks,

-- Steve

>  		kfree(enable_data);
>  	}

[1] https://sashiko.dev/#/patchset/20260723170212.55325-1-devnexen%40gmail.com