linux-kernel - Re: Instrumentation and RCU

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Message-ID: <20200312135339.GS12561@hirez.programming.kicks-ass.net>
Date:   Thu, 12 Mar 2020 14:53:39 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Jason Wessel <jason.wessel@...driver.com>
Subject: Re: Instrumentation and RCU

On Tue, Mar 10, 2020 at 12:43:27PM +0100, Thomas Gleixner wrote:
> That's why we want the sections and the annotation. If something calls
> out of a noinstr section into a regular text section and the call is not
> annotated at the call site, then objtool can complain and tell you. What
> Peter and I came up with looks like this:
> 
> noinstr foo()
> 	do_protected(); <- Safe because in the noinstr section
> 
> 	instr_begin();	<- Marks the begin of a safe region, ignored
>         		   by objtool
> 
>         do_stuff();     <- All good   
> 
>         instr_end();    <- End of the safe region. objtool starts
> 			   looking again
> 
>         do_other_stuff();  <- Unsafe because do_other_stuff() is
>         		      not protected
> and:
> 
> noinstr do_protected()
>         bar();		<- objtool will complain here
> 
> See?

Find here:

  https://lkml.kernel.org/r/20200312134107.700205216@infradead.org