linux-kernel - Re: [PATCH 4/4] tracing/uprobes: Fix the usage of uprobe_buffer_enable() in probe_event

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Date:	Mon, 30 Jun 2014 19:50:25 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Tom Zanussi <tom.zanussi@...ux.intel.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] tracing/uprobes: Fix the usage of
	uprobe_buffer_enable() in probe_event_enable()

On 06/30, Srikar Dronamraju wrote:
>
> > The usage of uprobe_buffer_enable() added by dcad1a20 is very wrong,
> >
> > 1. uprobe_buffer_enable() and uprobe_buffer_disable() are not balanced,
> >    _enable() should be called only if !enabled.
> >
> > 2. If uprobe_buffer_enable() fails probe_event_enable() should clear
> >    tp.flags and free event_file_link.
> >
> > 3. If uprobe_register() fails it should do uprobe_buffer_disable().
> >
> > Signed-off-by: Oleg Nesterov <oleg@...hat.com>
>
> Acked-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>

Thanks!

> (one nit .. )
>
> > +	ret = uprobe_buffer_enable();
> > +	if (ret)
> > +		goto err_flags;
> > +
> >  	tu->consumer.filter = filter;
> >  	ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
> > -	if (ret) {
> > -		if (file) {
> > -			list_del(&link->list);
> > -			kfree(link);
> > -			tu->tp.flags &= ~TP_FLAG_TRACE;
> > -		} else
> > -			tu->tp.flags &= ~TP_FLAG_PROFILE;
> > -	}
> > +	if (ret)
> > +		goto err_buffer;
> >
> > +	return 0;
> > +
> > + err_buffer:
> > +	uprobe_buffer_disable();
> > +
>
> How about avoiding err_buffer label?
> +	if (!ret)
> +		return 0;
>
> +	uprobe_buffer_disable();
> +

Well, I do not really mind. But to me it looks more consistent this way,
if-something-fail-goto-err_label.

IOW, I think that the code should either not use err-labels, or always
use them like above.

Besides, perhaps we will add "if (file) uprobe_apply()" after _register()
to mix perf/ftrace, then we will need to change this "if (!ret)" code again.

Oleg.

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