Re: [PATCH 2/2] tracing: Add free_trace_iter_content() helper function

[Zheng Yejian]

On 2023/7/13 23:47, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>
>
> 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@xxxxxxxxxxx>
> ---
>   kernel/trace/trace.c | 40 ++++++++++++++++++++++++++++------------
>   1 file changed, 28 insertions(+), 12 deletions(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 1c370ffbe062..3f38250637e2 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;
> @@ -6709,7 +6723,12 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp)
>   	}
>   
>   	trace_seq_init(&iter->seq);
> -	iter->trace = tr->current_trace;
> +
> +	iter->trace = kzalloc(sizeof(*iter->trace), GFP_KERNEL);
> +	if (!iter->trace)
> +		goto fail;

Hi, Steve, 'ret' may need to be set before `goto fail`:
  ret = -ENOMEM;

> +
> +	*iter->trace = *tr->current_trace;
>   
>   	if (!alloc_cpumask_var(&iter->started, GFP_KERNEL)) {
>   		ret = -ENOMEM;
> @@ -6763,10 +6782,7 @@ 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);