linux-kernel - Re: [PATCH] tracing: fix incorrect enabling of trace events by boot cmdline

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Message-ID: <20150417051053.GC25530@js1304-P5Q-DELUXE>
Date:	Fri, 17 Apr 2015 14:10:53 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing: fix incorrect enabling of trace events by boot
 cmdline

On Thu, Apr 16, 2015 at 09:39:52AM -0400, Steven Rostedt wrote:
> On Thu, 16 Apr 2015 13:44:44 +0900
> Joonsoo Kim <iamjoonsoo.kim@....com> wrote:
> 
> > There is a problem that trace events are not properly enabled with
> > boot cmdline. Problem is that if we pass "trace_event=kmem:mm_page_alloc"
> > to boot cmdline, it enables all kmem trace events.
> > 
> > It is caused by parsing mechanism. When we parse cmdline, buffer
> > contents is modified due to tokenization. And, if we use this buffer
> > again, we will get wrong result.
> > 
> > Unfortunately, this buffer should be accessed three times
> > to set trace events properly in boot time. So, we need to handle
> > this situation.
> > 
> > There is already handling code for ",", but, we need another for
> > ":". This patch add it.
> 
> Thanks, but your patch has a bug in it. I'll fix it up.
> 
> > 
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> > ---
> >  kernel/trace/trace_events.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> > index db54dda..ce5b194 100644
> > --- a/kernel/trace/trace_events.c
> > +++ b/kernel/trace/trace_events.c
> > @@ -565,6 +565,7 @@ static int __ftrace_set_clr_event(struct trace_array *tr, const char *match,
> >  static int ftrace_set_clr_event(struct trace_array *tr, char *buf, int set)
> >  {
> >  	char *event = NULL, *sub = NULL, *match;
> > +	int ret;
> >  
> >  	/*
> >  	 * The buf format can be <subsystem>:<event-name>
> > @@ -590,7 +591,11 @@ static int ftrace_set_clr_event(struct trace_array *tr, char *buf, int set)
> >  			event = NULL;
> >  	}
> >  
> > -	return __ftrace_set_clr_event(tr, match, sub, event, set);
> > +	ret = __ftrace_set_clr_event(tr, match, sub, event, set);
> > +
> > +	/* Put back the colon to allow this to be called again */
> > +	if (buf)
> > +		*(buf - 1) = ':';
> 
> You forgot to add:
> 
> 	return ret;
> 

Ah... my bad... :)
thanks for fixing it.

Thanks.
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