linux-kernel - Re: [PATCH] printk/tracing: Do not trace printk_nmi

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Message-ID: <20180907095344.75465afd@gandalf.local.home>
Date:   Fri, 7 Sep 2018 09:53:44 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH] printk/tracing: Do not trace printk_nmi_enter()

On Fri, 7 Sep 2018 11:30:55 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> > That said, I am not against this change. Especially the inlining
> > is a good move. Note that lockdep_off()/lockdep_on() must not
> > be traced as well.  
> 
> Hard to trace an inline funcion; we could make it __always_inline to
> feel better.

In the old days, you would need to make it __always_inline, because if
gcc didn't inline it (and it did so in the past), it would be traced
and would re-introduce this bug. But I've hit this issue too many times
in the past, that I added "notrace" to the "inline" definition, where
all "inline" labeled functions are also "notrace".

lockdep.o has the -pg option removed in the Makefile so that all
functions in lockdep.c is notrace, which is why it was fine to keep it
there.

But adding __always_inline may not be a bad idea regardless.

-- Steve