linux-kernel - Re: [PATCH] tracing: kprobe-event: Return directly when dyn_event

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Message-ID: <20260125232139.0e971011@robin>
Date: Sun, 25 Jan 2026 23:21:39 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: sunliming <sunliming@...ux.dev>
Cc: mhiramat@...nel.org, mathieu.desnoyers@...icios.com,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, sunliming
 <sunliming@...inos.cn>
Subject: Re: [PATCH] tracing: kprobe-event: Return directly when
 dyn_event_list is empty

On Mon, 26 Jan 2026 10:56:59 +0800
sunliming <sunliming@...ux.dev> wrote:

> During kernel boot, the setup_boot_kprobe_events() function causes
> significant delays, increasing overall startup time.
> 
> The root cause is a lock contention chain: its child function
> 
> enable_boot_kprobe_events() requires the event_mutex, which is already
> 
> held by early_event_add_tracer(). early_event_add_tracer() itself is 
> blocked

Ah, early_event_add_tracer() is called by the work function that sets
up tracers (and the event directories within them).

> 
> waiting for the trace_event_sem  read-write lock, which is held for an 
> extended
> 
>   period by trace_event_update_all(). trace_event_update_all()  is 
> runing in
> 
> eval_map_work_func() in   eval_map_wq.
> 
> On my ARM64 platform machine, the latency can reach around 200ms：
> 
> [ 0.268848] trace_kprobe: try_get_event_mutex 
> kernel/trace/tracekprobe.c,1902,enable_boot_kprobe_events
> [ 0.268849] try down_write 
> kernel/trace/traceevents.c,4114,early_event_add_tracer
> [ 0.482382] done up_write 
> kernel/trace/trace_events.c,3074,trace_event_eval_update
> [ 0.482386] done down_write 
> kernel/trace/trace_events.c,4116,early_event_add_tracer
> [ 0.482868] done up_write 
> kernel/trace/trace_events.c,4119,early_event_add_tracer
> [ 0.482877] trace_kprobe: enable_boot_kprobe_events geted eventmutex
> [ 0.482879] trace_kprobe: enable_bootk_probe_events release eventmutex

I take it that you are aware of this work, as it comes from someone
with the same email domain as you have.

  https://lore.kernel.org/all/20260122032051.386331-1-tianyaxiong@kylinos.cn/

That is moving the kprobe setup into the same work function.

-- Steve