linux-kernel - Re: [PATCH v4 1/3] livepatch: add (un)patch callbacks

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Date:   Wed, 30 Aug 2017 09:20:25 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Joe Lawrence <joe.lawrence@...hat.com>
Cc:     live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jessica Yu <jeyu@...nel.org>, Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Chris J Arges <chris.j.arges@...onical.com>
Subject: Re: [PATCH v4 1/3] livepatch: add (un)patch callbacks

On Wed, Aug 30, 2017 at 09:27:16AM -0400, Joe Lawrence wrote:
> > So instead of 'obj->pre_patch_callback_done', how about
> > 'obj->callbacks_enabled'?
> > 
> > It could be set in the following cases:
> > 
> >   a) if the object has a pre_patch callback, set obj->callbacks_enabled
> >      after the pre_patch callback succeeds; 
> > 
> >   b) else, if the patch does *not* have a pre_patch callback, set
> >      obj->callbacks_enabled after klp_patch_object() succeeds.
> > 
> > And the variable would need to be cleared after the post_unpatch
> > callback was run.
> > 
> > It's a bit complicated, but that seems to be the most logicial behavior
> > as far as I can tell.
> > 
> > Thoughts?
> 
> What if we flip it around as "callbacks_disabled"?  By default, kzalloc
> would init as false.  It would only be set to true if the pre-patch
> callback is provided and if it returns failure.  Would that reduce the
> number of conditions when we need to set this var?

Yeah, 'callbacks_disabled' sounds better.

> Also, as you noted, I think it would need to reset/cleared after the
> post-patch callback.  (For the livepatch-already-loaded cases.)

Since it can only be set when the pre-patch fails, I think it would only
need to be cleared after post-unpatch?

Or another alternative would be to unconditionally clear and/or set it
in klp_pre_patch_callback() so that its previous value doesn't matter.

-- 
Josh