linux-kernel - Re: barriers: was: [RFC PATCH v2 17/18] livepatch: change to a per-task consistency model

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Message-ID: <20160504170236.mpncog3iudr3cvem@treble>
Date:	Wed, 4 May 2016 12:02:36 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Petr Mladek <pmladek@...e.com>
Cc:	Jessica Yu <jeyu@...hat.com>, Jiri Kosina <jikos@...nel.org>,
	Miroslav Benes <mbenes@...e.cz>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
	x86@...nel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-s390@...r.kernel.org, Vojtech Pavlik <vojtech@...e.com>,
	Jiri Slaby <jslaby@...e.cz>,
	Chris J Arges <chris.j.arges@...onical.com>,
	Andy Lutomirski <luto@...nel.org>
Subject: Re: barriers: was: [RFC PATCH v2 17/18] livepatch: change to a
 per-task consistency model

On Wed, May 04, 2016 at 02:39:40PM +0200, Petr Mladek wrote:
> On Thu 2016-04-28 15:44:48, Josh Poimboeuf wrote:
> > Change livepatch to use a basic per-task consistency model.  This is the
> > foundation which will eventually enable us to patch those ~10% of
> > security patches which change function or data semantics.  This is the
> > biggest remaining piece needed to make livepatch more generally useful.
> 
> I spent a lot of time with checking the memory barriers. It seems that
> they are basically correct.  Let me use my own words to show how
> I understand it. I hope that it will help others with review.

[...snip a ton of useful comments...]

Thanks, this will help a lot!  I'll try to incorporate your barrier
comments into the code.

I also agree that kpatch_patch_task() is poorly named.  I was trying to
make it clear to external callers that "hey, the task is getting patched
now!", but it's internally inconsistent with livepatch code because we
make a distinction between patching and unpatching.

Maybe I'll do:

  klp_update_task_patch_state()

-- 
Josh