Re: How to recheck 'maxactive' ?

[Masami Hiramatsu <mhiramat@kernel.org>]

On Mon, 23 Mar 2020 09:04:01 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Mon, 23 Mar 2020 15:47:41 +0900
> Masami Hiramatsu <mhiramat@kernel.org> wrote:
> 
> > Hi Taeung,
> > 
> > On Sun, 22 Mar 2020 23:06:20 +0900
> > Taeung Song <treeze.taeung@gmail.com> wrote:
> > 
> > > Hi,
> > > 
> > > After setting 'maxactive' for kretprobe,
> > > how can I recheck the value of 'maxactive' ?
> > > For example, in order to distinguish the difference
> > > between two kretprobe events
> > > (kmem_cache_alloc_node and kmem_cache_alloc_node10)
> > > 
> > >    $ cd /sys/kernel/debug/tracing
> > >    $ echo 'r:kmem_cache_alloc_node kmem_cache_alloc_node' >> kprobe_events
> > >    $ echo 'r10:kmem_cache_alloc_node10 kmem_cache_alloc_node' >> 
> > > kprobe_events
> > > 
> > >    $ cat kprobe_events
> > >    r:kprobes/kmem_cache_alloc_node kmem_cache_alloc_node
> > >    r:kprobes/kmem_cache_alloc_node10 kmem_cache_alloc_node  
> > 
> > Oops! good catch. That must be a bug, since the kprobe_events design policy
> > is to support following operation.
> > 
> > $ cat kprobe_events > /etc/event_setting
> > (reboot)
> > $ cat /etc/event_setting > kprobe_events
> > 
> > What about below patch?
> > 
> > >From 935ed56819f2bfb7ac977f5c63273c9a6e3dfb42 Mon Sep 17 00:00:00 2001  
> > From: Masami Hiramatsu <mhiramat@kernel.org>
> > Date: Mon, 23 Mar 2020 10:57:48 +0900
> > Subject: [PATCH] ftrace/kprobe: Show the maxactive number on kprobe_events
> > 
> > Show maxactive parameter on kprobe_events.
> > This allows user to save the current configuration and
> > restore it without losing maxactive parameter.
> > 
> 
> Hi Masami,
> 
> Can you resend this patch as a stand alone (so that it shows up as a patch
> on the mailing lists).

Yes I'll do.

Thank you!

> 
> Thanks!
> 
> -- Steve
> 
> 
> > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> > ---
> >  kernel/trace/trace_kprobe.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> > index 362cca52f5de..d0568af4a0ef 100644
> > --- a/kernel/trace/trace_kprobe.c
> > +++ b/kernel/trace/trace_kprobe.c
> > @@ -1078,6 +1078,8 @@ static int trace_kprobe_show(struct seq_file *m, struct dyn_event *ev)
> >  	int i;
> >  
> >  	seq_putc(m, trace_kprobe_is_return(tk) ? 'r' : 'p');
> > +	if (trace_kprobe_is_return(tk) && tk->rp.maxactive)
> > +		seq_printf(m, "%d", tk->rp.maxactive);
> >  	seq_printf(m, ":%s/%s", trace_probe_group_name(&tk->tp),
> >  				trace_probe_name(&tk->tp));
> >  
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>