linux-kernel - Re: [PATCH v3 5/6] x86/ftrace: Use text

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Date:   Thu, 10 Oct 2019 09:19:56 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, mhiramat@...nel.org,
        bristot@...hat.com, jbaron@...mai.com,
        torvalds@...ux-foundation.org, tglx@...utronix.de,
        mingo@...nel.org, namit@...are.com, hpa@...or.com, luto@...nel.org,
        ard.biesheuvel@...aro.org, jpoimboe@...hat.com
Subject: Re: [PATCH v3 5/6] x86/ftrace: Use text_poke()

On Thu, 10 Oct 2019 11:20:54 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Wed, Oct 09, 2019 at 10:41:35PM -0400, Steven Rostedt wrote:
> > On Tue, 8 Oct 2019 10:43:35 -0400
> > Steven Rostedt <rostedt@...dmis.org> wrote:
> > 
> >   
> > > BTW, I'd really like to take this patch series through my tree. That
> > > way I can really hammer it, as well as I have code that will be built
> > > on top of it.  
> > 
> > I did a bit of hammering and found two bugs. One I sent a patch to fix
> > (adding a module when tracing is enabled), but the other bug I
> > triggered, I'm too tired to debug right now. But figured I'd mention it
> > anyway.  
> 
> I'm thinking this should fix it... Just not sure this is the right plce,
> then again, we're doing the same thing in jump_label and static_call, so
> perhaps we should do it like this.
> 
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -1230,10 +1230,15 @@ void text_poke_queue(void *addr, const v
>   * dynamically allocated memory. This function should be used when it is
>   * not possible to allocate memory.
>   */
> -void text_poke_bp(void *addr, const void *opcode, size_t len, const void *emulate)
> +void __ref text_poke_bp(void *addr, const void *opcode, size_t len, const void *emulate)
>  {
>  	struct text_poke_loc tp;
>  
> +	if (unlikely(system_state == SYSTEM_BOOTING)) {
> +		text_poke_early(addr, opcode, len);
> +		return;
> +	}

We need a new system state. SYSTEM_UP ? (Arg, that name is confusing,
SYSTEM_BOOTING_SMP?) Or perhaps just test num_online_cpus()?

	if (unlikely(system_state == SYSTEM_BOOTING &&
		     num_online_cpus() == 1)

?

Because we can't do the above once we have more than one CPU running.

-- Steve

> +
>  	text_poke_loc_init(&tp, addr, opcode, len, emulate);
>  	text_poke_bp_batch(&tp, 1);
>  }