linux-kernel - Re: [PATCH 2/6] x86: allow to call text_poke

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Message-ID: <20131019151658.583ac18e@gandalf.local.home>
Date:	Sat, 19 Oct 2013 15:16:58 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Petr Mladek <pmladek@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Kosina <jkosina@...e.cz>, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [PATCH 2/6] x86: allow to call text_poke_bp during boot

On Sun, 20 Oct 2013 00:02:32 +0900
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote:

> (2013/10/18 23:27), Petr Mladek wrote:
> > We would like to use text_poke_bp in ftrace. It might be called also during
> > boot when the interupts are disabled. We need to enable them for syncing
> > the cores on each CPU. Otherwise, there might be a deadlock, see the
> > warning in "smp_call_function_many", kernel/smp.c:371.
> 
> Steven, is this really needed?
> I think if this is the special use(e.g. boottime test),
> we'd better to run it after boot...
> 

It's used to convert the calls to mcount to nops. But maybe a better
thing to do is to check if we only have a single CPU:

static void run_sync(void)
{
	if (num_online_cpus() != 1)
		on_each_cpu(do_sync_core, NULL, 1);
}


I believe that the only time we call this function with interrupts
disabled is before SMP is set up. Thus, the above change would handle
that case.

-- Steve
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