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Date:   Tue, 26 Apr 2022 10:23:12 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Jakob Koschel <jakobkoschel@gmail.com>
Cc:     Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
        Mike Rapoport <rppt@kernel.org>,
        "Brian Johannesmeyer" <bjohannesmeyer@gmail.com>,
        Cristiano Giuffrida <c.giuffrida@vu.nl>,
        "Bos, H.J." <h.j.bos@vu.nl>
Subject: Re: [PATCH v2 2/4] tracing: Remove usage of list iterator variable
 after the loop
Message-ID: <20220426102312.70319297@gandalf.local.home>
In-Reply-To: <20220402103341.1763932-3-jakobkoschel@gmail.com>
References: <20220402103341.1763932-1-jakobkoschel@gmail.com>
        <20220402103341.1763932-3-jakobkoschel@gmail.com>
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On Sat,  2 Apr 2022 12:33:39 +0200
Jakob Koschel <jakobkoschel@gmail.com> wrote:

This patch crashed in my testing.

> @@ -1734,14 +1734,16 @@ static int subsystem_open(struct inode *inode, struct file *filp)
>  	/* Make sure the system still exists */
>  	mutex_lock(&event_mutex);
>  	mutex_lock(&trace_types_lock);
> -	list_for_each_entry(tr, &ftrace_trace_arrays, list) {
> -		list_for_each_entry(dir, &tr->systems, list) {
> -			if (dir == inode->i_private) {
> +	list_for_each_entry(iter_tr, &ftrace_trace_arrays, list) {
> +		list_for_each_entry(iter_dir, &iter_tr->systems, list) {
> +			if (iter_dir == inode->i_private) {
>  				/* Don't open systems with no events */
> -				if (dir->nr_events) {
> +				if (iter_dir->nr_events) {
>  					__get_system_dir(dir);
>  					system = dir->subsystem;

					system = NULL->subsystem


>  				}
> +				tr = iter_tr;
> +				dir = iter_dir;

But do not change that dir, move the setting above it. That is:

				tr = iter_tr;
				dir = iter_dir;
				if (iter_dir->nr_events) {
 					__get_system_dir(dir);
 					system = dir->subsystem;
				}

-- Steve

				
>  				goto exit_loop;
>  			}
>  		}