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Date:   Wed, 7 Sep 2022 17:51:36 +0900
From:   Masami Hiramatsu (Google) <mhiramat@kernel.org>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Jianlin Lv <iecedge@gmail.com>, corbet@lwn.net, mingo@redhat.com,
        jianlv@ebay.com, linux-kernel@vger.kernel.org,
        linux-doc@vger.kernel.org, Masami Hiramatsu <mhiramat@kernel.org>,
        Tom Zanussi <zanussi@kernel.org>, bpf@vger.kernel.org
Subject: Re: [PATCH v2] tracing/kprobes: Add method to display private
 kprobes in tracefs
Message-Id: <20220907175136.96b05b241e650de21eb661e6@kernel.org>
In-Reply-To: <20220906111214.0dd113cd@gandalf.local.home>
References: <20220725062334.1778-1-iecedge@gmail.com>
        <20220906111214.0dd113cd@gandalf.local.home>
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[Adding bpf ML]

On Tue, 6 Sep 2022 11:12:14 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> 
> [ Adding Masami and Tom ]
> 
> On Mon, 25 Jul 2022 06:23:34 +0000
> Jianlin Lv <iecedge@gmail.com> wrote:
> 
> > The private kprobes are not added to the global list dyn_event_list,
> > so there is a missing interface to show probe hit and probe miss.
> > This patch adds a profiling interface to check the number of hits or
> > misses for private kprobes.
> 
> Masami, what do you think of this patch?

I discussed it with BPF people when it was introduced and they didn't
want to show up it on tracefs because it is a private one. I agreed that.

So I think this kind of interface must be managed by BPF subsystem.
Is there any API to manage the BPF probe points in BPF subsystem?

Thank you,

> 
> -- Steve
> 
> > 
> > Signed-off-by: Jianlin Lv <iecedge@gmail.com>
> > ---
> > v2: update commit message
> > ---
> >  Documentation/trace/kprobetrace.rst |  6 +++-
> >  kernel/trace/trace_dynevent.c       | 20 +++++++++++
> >  kernel/trace/trace_dynevent.h       | 37 ++++++++++++++++++++
> >  kernel/trace/trace_kprobe.c         | 54 +++++++++++++++++++++++++++++
> >  4 files changed, 116 insertions(+), 1 deletion(-)
> > 
> > diff --git a/Documentation/trace/kprobetrace.rst b/Documentation/trace/kprobetrace.rst
> > index b175d88f31eb..8815d64dd8a6 100644
> > --- a/Documentation/trace/kprobetrace.rst
> > +++ b/Documentation/trace/kprobetrace.rst
> > @@ -146,7 +146,11 @@ trigger:
> >  Event Profiling
> >  ---------------
> >  You can check the total number of probe hits and probe miss-hits via
> > -/sys/kernel/debug/tracing/kprobe_profile.
> > +/sys/kernel/debug/tracing/kprobe_profile or
> > +/sys/kernel/debug/tracing/kprobe_local_profile.
> > +All kprobe events created by kprobe_events will be added to the global
> > +list, you can get their profiling via kprobe_profile; kprobe_local_profile
> > +shows profiling for private kprobe events created by perf_kprobe pmu.
> >  The first column is event name, the second is the number of probe hits,
> >  the third is the number of probe miss-hits.
> >  
> > diff --git a/kernel/trace/trace_dynevent.c b/kernel/trace/trace_dynevent.c
> > index 076b447a1b88..70ec99cd9c53 100644
> > --- a/kernel/trace/trace_dynevent.c
> > +++ b/kernel/trace/trace_dynevent.c
> > @@ -181,6 +181,26 @@ static const struct seq_operations dyn_event_seq_op = {
> >  	.show	= dyn_event_seq_show
> >  };
> >  
> > +#ifdef CONFIG_KPROBE_EVENTS
> > +LIST_HEAD(local_event_list);
> > +
> > +void *local_event_seq_start(struct seq_file *m, loff_t *pos)
> > +{
> > +	mutex_lock(&event_mutex);
> > +	return seq_list_start(&local_event_list, *pos);
> > +}
> > +
> > +void *local_event_seq_next(struct seq_file *m, void *v, loff_t *pos)
> > +{
> > +	return seq_list_next(v, &local_event_list, pos);
> > +}
> > +
> > +void local_event_seq_stop(struct seq_file *m, void *v)
> > +{
> > +	mutex_unlock(&event_mutex);
> > +}
> > +#endif /* CONFIG_KPROBE_EVENTS */
> > +
> >  /*
> >   * dyn_events_release_all - Release all specific events
> >   * @type:	the dyn_event_operations * which filters releasing events
> > diff --git a/kernel/trace/trace_dynevent.h b/kernel/trace/trace_dynevent.h
> > index 936477a111d3..e30193470295 100644
> > --- a/kernel/trace/trace_dynevent.h
> > +++ b/kernel/trace/trace_dynevent.h
> > @@ -101,6 +101,43 @@ void dyn_event_seq_stop(struct seq_file *m, void *v);
> >  int dyn_events_release_all(struct dyn_event_operations *type);
> >  int dyn_event_release(const char *raw_command, struct dyn_event_operations *type);
> >  
> > +#ifdef CONFIG_KPROBE_EVENTS
> > +extern struct list_head local_event_list;
> > +
> > +static inline
> > +int local_event_init(struct dyn_event *ev, struct dyn_event_operations *ops)
> > +{
> > +	if (!ev || !ops)
> > +		return -EINVAL;
> > +
> > +	INIT_LIST_HEAD(&ev->list);
> > +	ev->ops = ops;
> > +	return 0;
> > +}
> > +
> > +static inline int local_event_add(struct dyn_event *ev)
> > +{
> > +	lockdep_assert_held(&event_mutex);
> > +
> > +	if (!ev || !ev->ops)
> > +		return -EINVAL;
> > +
> > +	list_add_tail(&ev->list, &local_event_list);
> > +	return 0;
> > +}
> > +
> > +static inline void local_event_remove(struct dyn_event *ev)
> > +{
> > +	lockdep_assert_held(&event_mutex);
> > +	list_del_init(&ev->list);
> > +}
> > +
> > +void *local_event_seq_start(struct seq_file *m, loff_t *pos);
> > +void *local_event_seq_next(struct seq_file *m, void *v, loff_t *pos);
> > +void local_event_seq_stop(struct seq_file *m, void *v);
> > +
> > +#endif /* CONFIG_KPROBE_EVENTS */
> > +
> >  /*
> >   * for_each_dyn_event	-	iterate over the dyn_event list
> >   * @pos:	the struct dyn_event * to use as a loop cursor
> > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> > index a245ea673715..76f500b17b46 100644
> > --- a/kernel/trace/trace_kprobe.c
> > +++ b/kernel/trace/trace_kprobe.c
> > @@ -1213,6 +1213,52 @@ static const struct file_operations kprobe_profile_ops = {
> >  	.release        = seq_release,
> >  };
> >  
> > +#ifdef CONFIG_KPROBE_EVENTS
> > +/* kprobe Local profile  */
> > +static int local_probes_profile_seq_show(struct seq_file *m, void *v)
> > +{
> > +	struct dyn_event *ev = v;
> > +	struct trace_kprobe *tk;
> > +
> > +	if (!is_trace_kprobe(ev))
> > +		return 0;
> > +
> > +	tk = to_trace_kprobe(ev);
> > +	seq_printf(m, "  %-44s %15lu %15lu\n",
> > +		trace_probe_name(&tk->tp),
> > +		trace_kprobe_nhit(tk),
> > +		tk->rp.kp.nmissed);
> > +
> > +	return 0;
> > +}
> > +
> > +static const struct seq_operations local_profile_seq_op = {
> > +	.start  = local_event_seq_start,
> > +	.next   = local_event_seq_next,
> > +	.stop   = local_event_seq_stop,
> > +	.show   = local_probes_profile_seq_show
> > +};
> > +
> > +static int local_profile_open(struct inode *inode, struct file *file)
> > +{
> > +	int ret;
> > +
> > +	ret = security_locked_down(LOCKDOWN_TRACEFS);
> > +	if (ret)
> > +		return ret;
> > +
> > +	return seq_open(file, &local_profile_seq_op);
> > +}
> > +
> > +static const struct file_operations kprobe_local_profile_ops = {
> > +	.owner          = THIS_MODULE,
> > +	.open           = local_profile_open,
> > +	.read           = seq_read,
> > +	.llseek         = seq_lseek,
> > +	.release        = seq_release,
> > +};
> > +#endif /* CONFIG_KPROBE_EVENTS */
> > +
> >  /* Kprobe specific fetch functions */
> >  
> >  /* Return the length of string -- including null terminal byte */
> > @@ -1830,6 +1876,7 @@ create_local_trace_kprobe(char *func, void *addr, unsigned long offs,
> >  	if (ret < 0)
> >  		goto error;
> >  
> > +	local_event_add(&tk->devent);
> >  	return trace_probe_event_call(&tk->tp);
> >  error:
> >  	free_trace_kprobe(tk);
> > @@ -1849,6 +1896,7 @@ void destroy_local_trace_kprobe(struct trace_event_call *event_call)
> >  		return;
> >  	}
> >  
> > +	local_event_remove(&tk->devent);
> >  	__unregister_trace_kprobe(tk);
> >  
> >  	free_trace_kprobe(tk);
> > @@ -1929,6 +1977,12 @@ static __init int init_kprobe_trace(void)
> >  	trace_create_file("kprobe_profile", TRACE_MODE_READ,
> >  			  NULL, NULL, &kprobe_profile_ops);
> >  
> > +#ifdef CONFIG_KPROBE_EVENTS
> > +	/* kprobe Local profile */
> > +	tracefs_create_file("kprobe_local_profile", TRACE_MODE_READ,
> > +			  NULL, NULL, &kprobe_local_profile_ops);
> > +#endif /* CONFIG_KPROBE_EVENTS */
> > +
> >  	setup_boot_kprobe_events();
> >  
> >  	return 0;
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>