linux-kernel - Re: [for-next][PATCH 7/8] tracing/probe: Reject exactly same probe event

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Date:   Mon, 23 Sep 2019 16:12:53 +0530
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Naveen Rao <naveen.n.rao@...ux.vnet.ibm.com>,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Subject: Re: [for-next][PATCH 7/8] tracing/probe: Reject exactly same probe
 event

Hey Masami, Steven

>  
> +static bool trace_kprobe_has_same_kprobe(struct trace_kprobe *orig,
> +					 struct trace_kprobe *comp)
> +{
> +	struct trace_probe_event *tpe = orig->tp.event;
> +	struct trace_probe *pos;
> +	int i;
> +
> +	list_for_each_entry(pos, &tpe->probes, list) {
> +		orig = container_of(pos, struct trace_kprobe, tp);
> +		if (strcmp(trace_kprobe_symbol(orig),
> +			   trace_kprobe_symbol(comp)) ||
> +		    trace_kprobe_offset(orig) != trace_kprobe_offset(comp))
> +			continue;
> +
> +		/*
> +		 * trace_probe_compare_arg_type() ensured that nr_args and
> +		 * each argument name and type are same. Let's compare comm.
> +		 */
> +		for (i = 0; i < orig->tp.nr_args; i++) {
> +			if (strcmp(orig->tp.args[i].comm,
> +				   comp->tp.args[i].comm))
> +				continue;

In a nested loop, *continue* is going to continue iterating through the
inner loop. In which case, continue is doing nothing here. I thought we
should have used a goto instead. No?  To me, continue as a last statement of
a for loop always looks weird.

> +		}
> +
> +		return true;
> +	}

I think we need something like this:

	list_for_each_entry(pos, &tpe->probes, list) {
		orig = container_of(pos, struct trace_kprobe, tp);
		if (strcmp(trace_kprobe_symbol(orig),
			   trace_kprobe_symbol(comp)) ||
		    trace_kprobe_offset(orig) != trace_kprobe_offset(comp))
			continue;

		/*
		 * trace_probe_compare_arg_type() ensured that nr_args and
		 * each argument name and type are same. Let's compare comm.
		 */
		for (i = 0; i < orig->tp.nr_args; i++) {
			if (strcmp(orig->tp.args[i].comm,
				   comp->tp.args[i].comm))
				goto outer_loop;

		}

		return true;
outer_loop:
	}


> +
> +	return false;
> +}
> +
>  

......

> +static bool trace_uprobe_has_same_uprobe(struct trace_uprobe *orig,
> +					 struct trace_uprobe *comp)
> +{
> +	struct trace_probe_event *tpe = orig->tp.event;
> +	struct trace_probe *pos;
> +	struct inode *comp_inode = d_real_inode(comp->path.dentry);
> +	int i;
> +
> +	list_for_each_entry(pos, &tpe->probes, list) {
> +		orig = container_of(pos, struct trace_uprobe, tp);
> +		if (comp_inode != d_real_inode(orig->path.dentry) ||
> +		    comp->offset != orig->offset)
> +			continue;
> +
> +		/*
> +		 * trace_probe_compare_arg_type() ensured that nr_args and
> +		 * each argument name and type are same. Let's compare comm.
> +		 */
> +		for (i = 0; i < orig->tp.nr_args; i++) {
> +			if (strcmp(orig->tp.args[i].comm,
> +				   comp->tp.args[i].comm))
> +				continue;

Same as above.

> +		}
> +
> +		return true;
> +	}
> +
> +	return false;
> +}
> +

-- 
Thanks and Regards
Srikar Dronamraju