Re: [PATCH v5 2/6] tracing: Fix to check event_mutex is held while accessing trigger list

[Steven Rostedt]

On Sun,  4 Sep 2022 13:12:29 +0900
"Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> 
> Since the check_user_trigger() is called outside of RCU
> read lock, this list_for_each_entry_rcu() caused a suspicious
> RCU usage warning.
> 
>  # echo hist:keys=pid > events/sched/sched_stat_runtime/trigger
>  # cat events/sched/sched_stat_runtime/trigger
> [   43.167032]
> [   43.167418] =============================
> [   43.167992] WARNING: suspicious RCU usage
> [   43.168567] 5.19.0-rc5-00029-g19ebe4651abf #59 Not tainted
> [   43.169283] -----------------------------
> [   43.169863] kernel/trace/trace_events_trigger.c:145 RCU-list traversed in non-reader section!!
> ...
> 
> However, this file->triggers list is safe when it is accessed
> under event_mutex is held.
> To fix this warning, adds a lockdep_is_held check to the
> list_for_each_entry_rcu().
> 
> Fixes: 7491e2c44278 ("tracing: Add a probe that attaches to trace events")
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> ---

I'm going to pull this patch out of these series, mark it for stable, and
add it to my queue that is going to Linus.

-- Steve