linux-kernel - Re: [PATCH -v5 05/17] x86/ftrace: Use text

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Message-ID: <20191112222413.GB4131@hirez.programming.kicks-ass.net>
Date:   Tue, 12 Nov 2019 23:24:13 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.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, jeyu@...nel.org,
        alexei.starovoitov@...il.com
Subject: Re: [PATCH -v5 05/17] x86/ftrace: Use text_poke()

On Tue, Nov 12, 2019 at 01:25:36PM -0500, Steven Rostedt wrote:
> On Mon, 11 Nov 2019 14:12:57 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:

> >  int ftrace_arch_code_modify_post_process(void)
> >      __releases(&text_mutex)
> >  {
> > -	set_all_modules_text_ro();
> > -	set_kernel_text_ro();
> > +	text_poke_finish();
> 
> Why is the text_poke_finish() needed here? Can we add a comment about
> why?

I think this is because of the text_poke_queue() in
ftrace_modify_code_direct(). I seem to have forgotten the code-flow
between the core and arch parts of ftrace again.

But sure, I can try and dig that out again and write a comment.


> > +	text_poke_bp((void *)ip, new, MCOUNT_INSN_SIZE, NULL); // BATCH
> 
> What do you mean by "BATCH" ?

Ah, that was a question, can/should we use text_poke_queue() there?