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Date:   Wed, 27 Jan 2021 22:27:43 +0900
From:   Masami Hiramatsu <mhiramat@kernel.org>
To:     Jianlin Lv <Jianlin.Lv@arm.com>
Cc:     Oleg Nesterov <oleg@redhat.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3] tracing: precise log info for kretprobe addr err
Message-Id: <20210127222743.771338cf7f89fb0b78dd838c@kernel.org>
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On Wed, 27 Jan 2021 02:46:10 +0000
Jianlin Lv <Jianlin.Lv@arm.com> wrote:

> 
> 
> > -----Original Message-----
> > From: Masami Hiramatsu <mhiramat@kernel.org>
> > Sent: Wednesday, January 27, 2021 10:02 AM
> > To: Oleg Nesterov <oleg@redhat.com>
> > Cc: Steven Rostedt <rostedt@goodmis.org>; Jianlin Lv <Jianlin.Lv@arm.com>;
> > mingo@redhat.com; linux-kernel@vger.kernel.org
> > Subject: Re: [PATCH v3] tracing: precise log info for kretprobe addr err
> >
> > On Tue, 26 Jan 2021 21:20:59 +0100
> > Oleg Nesterov <oleg@redhat.com> wrote:
> >
> > > On 01/26, Masami Hiramatsu wrote:
> > > >
> > > > > >
> > > > > > IOW, the "offset != 0" check removed by this patch is obviously wrong,
> > right?
> > > > > >
> > > >
> > > > No, not wrong. Even offset != 0, if the symbol exists in the kernel,
> > > > kprobe_on_func_entry() will check it.
> > >
> > > Yes, but unless I am totally confused... if kprobe_on_func_entry()
> > > returns false, then trace_kprobe_create() should fail with BAD_RETPROBE
> > even if offset == 0 ?
> >
> > Yes, if kprobe_on_func_entry() returns false, register_kretprobe() also
> > returns an error.
> >
> > -----
> > int register_kretprobe(struct kretprobe *rp) {
> >         int ret = 0;
> >         struct kretprobe_instance *inst;
> >         int i;
> >         void *addr;
> >
> >         if (!kprobe_on_func_entry(rp->kp.addr, rp->kp.symbol_name, rp-
> > >kp.offset))
> >                 return -EINVAL;
> >
> > -----
> >
> > Thank you,
> >
> > --
> > Masami Hiramatsu <mhiramat@kernel.org>
> 
> 
> If register_kretprobe()returns an error -EINVAL.
> This means that __register_trace_kprobe return -EINVAL,
> 
> ---
> ret = __register_trace_kprobe(tk);
> if (ret == -ENOENT && !trace_kprobe_module_exist(tk)) {
> pr_warn("This probe might be able to register after target module is loaded. Continue.\n");
> ret = 0;
> }
> ---
> As code show, cannot enable kretprobe for an unloaded module.
> 
> This is consistent with my test results (no VXLAN module is loaded).
> 
> # perf probe -m /lib/modules/5.11.0-rc2+/kernel/drivers/net/vxlan.ko  \
> 'vxlan_xmit%return $retval'
> Failed to write event: Invalid argument
>   Error: Failed to add events.
> 
> Is this a bug?

Oops, good catch!
It seems that the bug has been introduced when I added kprobe_on_func_entry() to register_Kretprobe.
Let me fix it.

Thank you!


-- 
Masami Hiramatsu <mhiramat@kernel.org>