Re: [PATCH v2] tracing/uprobes: Support ftrace_event_file base multibuffer

[Oleg Nesterov <oleg@redhat.com>]

Hi Jovi,

I'll try to read this patch carefully tomorrow.

Looks fine at first glance, but some nits below.

On 06/24, zhangwei(Jovi) wrote:
>
>  static int uprobe_trace_func(struct trace_uprobe *tu, struct pt_regs *regs)
>  {
> -	if (!is_ret_probe(tu))
> -		uprobe_trace_print(tu, 0, regs);
> +	struct event_file_link *link;
> +
> +	if (is_ret_probe(tu))
> +		return 0;
> +
> +	rcu_read_lock();
> +
> +	list_for_each_entry(link, &tu->files, list)
> +		uprobe_trace_print(tu, 0, regs, link->file);
> +
> +	rcu_read_unlock();

Purely cosmetic and I won't argue, but why the empty lines around
list_for_each_entry() ?

>  static int
> -probe_event_enable(struct trace_uprobe *tu, int flag, filter_func_t filter)
> +probe_event_enable(struct trace_uprobe *tu, struct ftrace_event_file *file,
> +		   filter_func_t filter)
>  {
> +	int enabled = 0;
>  	int ret = 0;
> 
> -	if (is_trace_uprobe_enabled(tu))
> +	/*
> +	 * Currently TP_FLAG_TRACE/TP_FLAG_PROFILE are mutually exclusive
> +	 * for uprobe(filter argument issue), this need to fix in future.
> +	 */
> +	if ((file && (tu->flags & TP_FLAG_PROFILE)) ||
> +	    (!file && (tu->flags & TP_FLAG_TRACE)))
>  		return -EINTR;

Well, this looks confusing and overcomplicated, see below.

> +	/* Currently we cannot call uprobe_register twice for same tu */
> +	if (is_trace_uprobe_enabled(tu))
> +		enabled = 1;

The comment is wrong. It is not that we can't do this "Currently".

We must not do uprobe_register(..., consumer) twice, consumer/uprobe
are linked together.

> +	if (file) {
> +		struct event_file_link *link;
> +

Just add
		if (TP_FLAG_PROFILE)
			return -EINTR;

here and kill the complicated check below. Same for the "else" branch.

> +static void
> +probe_event_disable(struct trace_uprobe *tu, struct ftrace_event_file *file)
> +{
> +	if (file) {
> +		struct event_file_link *link;
> +
> +		link = find_event_file_link(tu, file);
> +		if (!link)
> +			return;
> +
> +		list_del_rcu(&link->list);
> +		/* synchronize with uprobe_trace_func/uretprobe_trace_func */
> +		synchronize_sched();
> +		kfree(link);
> +
> +		if (!list_empty(&tu->files))
> +			return;
> +
> +		tu->flags &= ~TP_FLAG_TRACE;
> +	} else
> +		tu->flags &= ~TP_FLAG_PROFILE;
> +
> 
>  	WARN_ON(!uprobe_filter_is_empty(&tu->filter));
> 
> -	uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
> -	tu->flags &= ~flag;
> +	if (!is_trace_uprobe_enabled(tu))
> +		uprobe_unregister(tu->inode, tu->offset, &tu->consumer);

Well, this is not exactly right... Currently this is fine, but still.

It would be better to clear TP_FLAG_TRACE/TP_FLAG_PROFILE after
uprobe_unregister(), when we can't race with the running handler
which can check ->flags.

And I'd suggest you to send the soft-enable/disable change in a
separate (and trivial) patch.

Oleg.