linux-kernel - Re: [PATCH v1] tracing/kprobes: expose maxactive for kretprobe in kprobe

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Date:   Wed, 29 Mar 2017 08:44:35 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Alban Crequy <alban.crequy@...il.com>,
        Alban Crequy <alban@...volk.io>,
        Alexei Starovoitov <ast@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Omar Sandoval <osandov@...com>, linux-doc@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        iago@...volk.io, michael@...volk.io,
        "Dorau, Lukasz" <lukasz.dorau@...el.com>
Subject: Re: [PATCH v1] tracing/kprobes: expose maxactive for kretprobe in
 kprobe_events

On Tue, 28 Mar 2017 11:34:07 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Wed, 29 Mar 2017 00:23:35 +0900
> Masami Hiramatsu <mhiramat@...nel.org> wrote:
> 
> > > @@ -598,8 +601,10 @@ static int create_trace_kprobe(int argc, char **argv)
> > >  {
> > >  	/*
> > >  	 * Argument syntax:
> > > -	 *  - Add kprobe: p[:[GRP/]EVENT] [MOD:]KSYM[+OFFS]|KADDR [FETCHARGS]
> > > -	 *  - Add kretprobe: r[:[GRP/]EVENT] [MOD:]KSYM[+0] [FETCHARGS]
> > > +	 *  - Add kprobe:
> > > +	 *      p[:[GRP/]EVENT] [MOD:]KSYM[+OFFS]|KADDR [FETCHARGS]
> > > +	 *  - Add kretprobe:
> > > +	 *      r[MAXACTIVE][:[GRP/]EVENT] [MOD:]KSYM[+0] [FETCHARGS]
> > >  	 * Fetch args:
> > >  	 *  $retval	: fetch return value
> > >  	 *  $stack	: fetch stack address
> > > @@ -619,6 +624,7 @@ static int create_trace_kprobe(int argc, char **argv)
> > >  	int i, ret = 0;
> > >  	bool is_return = false, is_delete = false;
> > >  	char *symbol = NULL, *event = NULL, *group = NULL;
> > > +	int maxactive = 0;
> > >  	char *arg;
> > >  	unsigned long offset = 0;
> > >  	void *addr = NULL;
> > > @@ -637,8 +643,26 @@ static int create_trace_kprobe(int argc, char **argv)
> > >  		return -EINVAL;
> > >  	}
> > >  
> > > -	if (argv[0][1] == ':') {
> > > +	if (is_return && isdigit(argv[0][1]) && strchr(&argv[0][1], ':')) {  
> > 
> > This only supports r[MAXACTIVE:[GRP/]EVENT]. e.g "r100" without event name.
> 
> You mean it doesn't support adding MAXACTIVE without the ':event'.

Yeah, sorry for lacking the explanation...

> 
> > 
> > Thank you,
> > 
> > > +		event = strchr(&argv[0][1], ':') + 1;
> > > +		event[-1] = '\0';
> > > +		ret = kstrtouint(&argv[0][1], 0, &maxactive);
> > > +		if (ret) {
> > > +			pr_info("Failed to parse maxactive.\n");
> > > +			return ret;
> > > +		}
> > > +		/* kretprobes instances are iterated over via a list. The
> > > +		 * maximum should stay reasonable.
> > > +		 */
> > > +		if (maxactive > 1024) {
> 
> Also, can we get rid of magic numbers within the code. There should be a
> const or macro defined as MAX_MAXACTIVE or something, and use that here.

Good catch!

Thanks,

> 
> -- Steve
> 
> 
> > > +			pr_info("Maxactive is too big.\n");
> > > +			return -EINVAL;
> > > +		}
> > > +	} else if (argv[0][1] == ':') {
> > >  		event = &argv[0][2];
> > > +	}
> > > +
> > > +	if (event) {
> > >  		if (strchr(event, '/')) {
> > >  			group = event;
> > >  			event = strchr(group, '/') + 1;
> > > @@ -718,8 +742,8 @@ static int create_trace_kprobe(int argc, char **argv)
> > >  				 is_return ? 'r' : 'p', addr);
> > >  		event = buf;
> > >  	}
> > > -	tk = alloc_trace_kprobe(group, event, addr, symbol, offset, argc,
> > > -			       is_return);
> > > +	tk = alloc_trace_kprobe(group, event, addr, symbol, offset, maxactive,
> > > +			       argc, is_return);
> > >  	if (IS_ERR(tk)) {
> > >  		pr_info("Failed to allocate trace_probe.(%d)\n",
> > >  			(int)PTR_ERR(tk));
> > > -- 
> > > 2.7.4
> > >   
> > 
> > 
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>