linux-kernel - Re: [PATCH v2 2/4] tracing: Remove usage of list iterator variable after the loop

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Message-ID: <20220426102312.70319297@gandalf.local.home>
Date:   Tue, 26 Apr 2022 10:23:12 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Jakob Koschel <jakobkoschel@...il.com>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Mike Rapoport <rppt@...nel.org>,
        "Brian Johannesmeyer" <bjohannesmeyer@...il.com>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>
Subject: Re: [PATCH v2 2/4] tracing: Remove usage of list iterator variable
 after the loop

On Sat,  2 Apr 2022 12:33:39 +0200
Jakob Koschel <jakobkoschel@...il.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;
>  			}
>  		}