linux-kernel - Re: [PATCH v2 09/13] notifier: Show function names on notifier routines if DEBUG

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Date:   Tue, 19 Jul 2022 13:33:13 -0700
From:   Arjan van de Ven <arjan@...ux.intel.com>
To:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        akpm@...ux-foundation.org, bhe@...hat.com, pmladek@...e.com,
        kexec@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org,
        netdev@...r.kernel.org, x86@...nel.org, kernel-dev@...lia.com,
        kernel@...ccoli.net, halves@...onical.com, fabiomirmar@...il.com,
        alejandro.j.jimenez@...cle.com, andriy.shevchenko@...ux.intel.com,
        arnd@...db.de, bp@...en8.de, corbet@....net,
        d.hatayama@...fujitsu.com, dave.hansen@...ux.intel.com,
        dyoung@...hat.com, feng.tang@...el.com, gregkh@...uxfoundation.org,
        mikelley@...rosoft.com, hidehiro.kawai.ez@...achi.com,
        jgross@...e.com, john.ogness@...utronix.de, keescook@...omium.org,
        luto@...nel.org, mhiramat@...nel.org, mingo@...hat.com,
        paulmck@...nel.org, peterz@...radead.org, rostedt@...dmis.org,
        senozhatsky@...omium.org, stern@...land.harvard.edu,
        tglx@...utronix.de, vgoyal@...hat.com, vkuznets@...hat.com,
        will@...nel.org, Cong Wang <xiyou.wangcong@...il.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Valentin Schneider <valentin.schneider@....com>,
        Xiaoming Ni <nixiaoming@...wei.com>
Subject: Re: [PATCH v2 09/13] notifier: Show function names on notifier
 routines if DEBUG_NOTIFIERS is set

On 7/19/2022 12:53 PM, Guilherme G. Piccoli wrote:
> Currently we have a debug infrastructure in the notifiers file, but
> it's very simple/limited. Extend it by:
> 
> (a) Showing all registered/unregistered notifiers' callback names;


I'm not yet convinced that this is the right direction.
The original intent for this "debug" feature was to be lightweight enough that it could run in production, since at the time, rootkits
liked to clobber/hijack notifiers and there were also some other signs of corruption at the time.

By making something print (even at pr_info) for what are probably frequent non-error operations, you turn something that is light
into something that's a lot more heavy and generally that's not a great idea... it'll be a performance surprise.