linux-kernel - Re: suspicious RCU usage warning on tracing/urgent

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Message-ID: <20230911170929.1b0ede14@gandalf.local.home>
Date:   Mon, 11 Sep 2023 17:09:29 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc:     Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: suspicious RCU usage warning on tracing/urgent

On Mon, 11 Sep 2023 12:00:53 +0900
Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:

> But it seems correctly taking srcu_read_lock().
> 
>     452 
>     453         ei = ti->private;
>     454         idx = srcu_read_lock(&eventfs_srcu);
>     455         list_for_each_entry_rcu(ef, &ei->e_top_files, list) {
>     456                 create_dentry(ef, dentry, false);
>     457         }
>     458         srcu_read_unlock(&eventfs_srcu, idx);
>     459         return dcache_dir_open(inode, file);
>     460 }
>     461 
> 
> This may false-positive warning, or srcu_read_lock() is not enough for
> list_for_each_entry_rcu(). In latter case, maybe we need to use a
> mutex instead of srcu for update the ef.

Oops, that should be list_for_each_entry_srcu().

Thanks!

> 
> BTW, the ftracetest itself passed without any problem.

Thanks for testing as well!

-- Steve