linux-kernel - Re: [RFC][PATCH 4/4] tracing/uprobes: Fail to unregister if probe event files are open

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Date:	Thu, 01 Aug 2013 10:25:54 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC][PATCH 4/4] tracing/uprobes: Fail to unregister if probe
 event files are open

On Thu, 2013-08-01 at 16:08 +0200, Oleg Nesterov wrote:
> On 07/03, Steven Rostedt wrote:
> >
> > From: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>
> 
> Acked-by: Oleg Nesterov <oleg@...hat.com>

Thanks!

> 
> 
> Just a couple of nits in the case you are going to redo this change,
> 
> > Modules do with with the module owner set (automated
> > from the VFS layer).
> 
> This logic is dead, I think.
> 
> > The ftrace buffer instances have a ref count added
> > to the trace_array when the enabled file is opened
> 
> This is too.
> 

Yeah, the change log needs an update.

> > -static void cleanup_all_probes(void)
> > +static int cleanup_all_probes(void)
> >  {
> >  	struct trace_uprobe *tu;
> > +	int ret = 0;
> >  
> >  	mutex_lock(&uprobe_lock);
> >  	while (!list_empty(&uprobe_list)) {
> >  		tu = list_entry(uprobe_list.next, struct trace_uprobe, list);
> > -		unregister_trace_uprobe(tu);
> > +		ret = unregister_trace_uprobe(tu);
> > +		if (ret)
> > +			break;
> >  	}
> >  	mutex_unlock(&uprobe_lock);
> > +	return ret;
> >  }
> 
> Again, it is not clear what exactly we should do and I won't argue
> either way. But note that (with or without this patch) this doesn't
> match kprobe's release_all_trace_probes() which checks (tries to,
> actually) trace_probe_is_enabled() for every probe first. Perhaps
> we should cleanup this later.

Agreed on all accounts. Especially the "we should cleanup this later"
part ;-)

> 
> >  static int probes_open(struct inode *inode, struct file *file)
> >  {
> > +	int ret = 0;
> > +
> >  	if ((file->f_mode & FMODE_WRITE) && (file->f_flags & O_TRUNC))
> > -		cleanup_all_probes();
> > +		ret = cleanup_all_probes();
> > +	if (ret)
> > +		return ret;
> 
> Cosmetic, but perhaps it would be a bit more clean to move this check
> (with "int ret") under if (WRITE && TRUNC) block.
> 

Yeah, agreed.

-- Steve


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