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

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Message-ID: <20220906220904.1abd4610@gandalf.local.home>
Date:   Tue, 6 Sep 2022 22:09:04 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc:     Tom Zanussi <zanussi@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 2/6] tracing: Fix to check event_mutex is held while
 accessing trigger list

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

> From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> 
> 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@...nel.org>
> ---

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