Re: [PATCH v3] tracing: Fix race between update_event_fields and event_define_fields

[Steven Rostedt <rostedt@goodmis.org>]

On Fri, 31 Jul 2026 11:41:02 +0800
Michael Wu <michael@allwinnertech.com> wrote:

> An alternative of placing mutex_lock inside update_event_fields() was
> considered but rejected -- it would invert the established lock
> ordering (trace_event_sem -> event_mutex) and risk ABBA deadlock.
> 
> Fixes: b3bc8547d3be ("tracing: Have TRACE_DEFINE_ENUM affect trace event 
> types as well")
> Cc: stable@vger.kernel.org
> Signed-off-by: Michael Wu <michael@allwinnertech.com>
> ---
>   kernel/trace/trace_events.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 956692856fa8..9632788da5af 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -3566,6 +3566,7 @@ void trace_event_update_all(struct trace_eval_map 
> **map, int len)
>          int last_i;
>          int i;
> 
> +       mutex_lock(&event_mutex);
>          down_write(&trace_event_sem);
>          list_for_each_entry_safe(call, p, &ftrace_events, list) {
>                  /* events are usually grouped together with systems */
> @@ -3604,6 +3605,7 @@ void trace_event_update_all(struct trace_eval_map 
> **map, int len)
>                  cond_resched();
>          }
>          up_write(&trace_event_sem);
> +       mutex_unlock(&event_mutex);
>   }
> 
>   static bool event_in_systems(struct trace_event_call *call,

You need to fix your email client to not mangle the output. It replaced
tabs with spaces and wrapped text, making it so I can not apply the patch.

-- Steve