Re: How to recheck 'maxactive' ?

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Hi Masami,

Thank you for the reply!
And your patch looks great.


On 3/23/20 3:47 PM, Masami Hiramatsu wrote:
Hi Taeung,

On Sun, 22 Mar 2020 23:06:20 +0900
Taeung Song <treeze.taeung@xxxxxxxxx> wrote:


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' >>

    $ 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
$ cat /etc/event_setting > kprobe_events

What about below patch?

 From 935ed56819f2bfb7ac977f5c63273c9a6e3dfb42 Mon Sep 17 00:00:00 2001
From: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
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.

Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
  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),

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