linux-kernel - Re: [PATCH v2 2/2] tracing: Add free_trace_iter

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Message-Id: <20230726224213.f5f3a23d207ffedeee291d22@kernel.org>
Date:   Wed, 26 Jul 2023 22:42:13 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 2/2] tracing: Add free_trace_iter_content() helper
 function

On Sat, 15 Jul 2023 10:12:15 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
> 
> As the trace iterator is created and used by various interfaces, the clean
> up of it needs to be consistent. Create a free_trace_iter_content() helper
> function that frees the content of the iterator and use that to clean it
> up in all places that it is used.
> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>

Looks good to me.

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

BTW, this adds iter->fmt != static_fmt_buf check. Is it a kind of fix?

Thank you,

> ---
>  kernel/trace/trace.c | 33 ++++++++++++++++++++++-----------
>  1 file changed, 22 insertions(+), 11 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 1c370ffbe062..8775930aa545 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -4815,6 +4815,25 @@ static const struct seq_operations tracer_seq_ops = {
>  	.show		= s_show,
>  };
>  
> +/*
> + * Note, as iter itself can be allocated and freed in different
> + * ways, this function is only used to free its content, and not
> + * the iterator itself. The only requirement to all the allocations
> + * is that it must zero all fields (kzalloc), as freeing works with
> + * ethier allocated content or NULL.
> + */
> +static void free_trace_iter_content(struct trace_iterator *iter)
> +{
> +	/* The fmt is either NULL, allocated or points to static_fmt_buf */
> +	if (iter->fmt != static_fmt_buf)
> +		kfree(iter->fmt);
> +
> +	kfree(iter->temp);
> +	kfree(iter->buffer_iter);
> +	mutex_destroy(&iter->mutex);
> +	free_cpumask_var(iter->started);
> +}
> +
>  static struct trace_iterator *
>  __tracing_open(struct inode *inode, struct file *file, bool snapshot)
>  {
> @@ -4922,8 +4941,7 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot)
>  
>   fail:
>  	mutex_unlock(&trace_types_lock);
> -	kfree(iter->temp);
> -	kfree(iter->buffer_iter);
> +	free_trace_iter_content(iter);
>  release:
>  	seq_release_private(inode, file);
>  	return ERR_PTR(-ENOMEM);
> @@ -5002,11 +5020,7 @@ static int tracing_release(struct inode *inode, struct file *file)
>  
>  	mutex_unlock(&trace_types_lock);
>  
> -	mutex_destroy(&iter->mutex);
> -	free_cpumask_var(iter->started);
> -	kfree(iter->fmt);
> -	kfree(iter->temp);
> -	kfree(iter->buffer_iter);
> +	free_trace_iter_content(iter);
>  	seq_release_private(inode, file);
>  
>  	return 0;
> @@ -6763,10 +6777,7 @@ static int tracing_release_pipe(struct inode *inode, struct file *file)
>  
>  	mutex_unlock(&trace_types_lock);
>  
> -	free_cpumask_var(iter->started);
> -	kfree(iter->fmt);
> -	kfree(iter->temp);
> -	mutex_destroy(&iter->mutex);
> +	free_trace_iter_content(iter);
>  	kfree(iter);
>  
>  	trace_array_put(tr);
> -- 
> 2.40.1


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