linux-kernel - Re: [PATCH -printk] printk, tracing: fix console tracepoint

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Date:   Tue, 12 Jul 2022 10:53:53 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Marco Elver <elver@...gle.com>,
        John Ogness <john.ogness@...utronix.de>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        Thomas Gleixner <tglx@...utronix.de>,
        Johannes Berg <johannes.berg@...el.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Linux Kernel Functional Testing <lkft@...aro.org>
Subject: Re: [PATCH -printk] printk, tracing: fix console tracepoint

On Tue, 12 Jul 2022 06:49:16 -0700
"Paul E. McKenney" <paulmck@...nel.org> wrote:

> > I guess the question is, can we have printk() in such a place? Because this
> > tracepoint is attached to printk and where ever printk is done so is this
> > tracepoint.  
> 
> As I understand it, code in such a place should be labeled noinstr.
> Then the call to printk() would be complained about as an illegal
> noinstr-to-non-noinstr call.
> 
> But where exactly is that printk()?

Perhaps the fix is to remove the _rcuidle() from trace_console_rcuidle().
If printk() can never be called from noinstr (aka RCU not watching).

-- Steve