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

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Message-ID: <20191015134228.GJ2328@hirez.programming.kicks-ass.net>
Date:   Tue, 15 Oct 2019 15:42:28 +0200
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
Subject: Re: [PATCH v3 5/6] x86/ftrace: Use text_poke()

On Tue, Oct 15, 2019 at 09:28:02AM -0400, Steven Rostedt wrote:
> On Fri, 11 Oct 2019 14:59:03 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Thu, Oct 10, 2019 at 07:28:19PM +0200, Peter Zijlstra wrote:
> > 
> > > Really the best solution is to move all the poking into
> > > ftrace_module_init(), before we mark it RO+X. That's what I'm going to
> > > do for jump_label and static_call as well, I just need to add that extra
> > > notifier callback.  
> > 
> > OK, so I started writing that patch... or rather, I wrote the patch and
> > started on the Changelog when I ran into trouble describing why we need
> > it.
> > 
> > That is, I'm struggling to explain why we cannot flip
> > prepare_coming_module() and complete_formation().
> > 
> > Yes, it breaks ftrace, but I'm thinking that is all it breaks. So let me
> > see if we can cure that.
> 
> You are mainly worried about making text that is executable into
> read-write again. What if we kept my one patch that just changed the
> module in ftrace_module_enable() from read-only to read-write, but
> before we ever set it executable.

This still flips the protections back and forth, which is still really
ugly. And afaict the only reason this is required is that
set_all_modules_text_*() stuff.

So please, instead of tinkering around, lets just kill that horrible
interface and be done with it. There's only 2 users left, fixing those
can't be too hard.