linux-kernel - Re: [PATCH v14 05/11] livepatch: Simplify API by removing registration step

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Date:   Thu, 13 Dec 2018 16:29:59 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Joe Lawrence <joe.lawrence@...hat.com>
Cc:     Petr Mladek <pmladek@...e.com>, Miroslav Benes <mbenes@...e.cz>,
        Jiri Kosina <jikos@...nel.org>,
        Jason Baron <jbaron@...mai.com>,
        Evgenii Shatokhin <eshatokhin@...tuozzo.com>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v14 05/11] livepatch: Simplify API by removing
 registration step

On Thu, Dec 06, 2018 at 09:36:06AM -0500, Joe Lawrence wrote:
> On 12/06/2018 05:14 AM, Petr Mladek wrote:
> > On Thu 2018-12-06 10:23:40, Miroslav Benes wrote:
> >> On Thu, 6 Dec 2018, Petr Mladek wrote:
> >>
> >>> On Wed 2018-12-05 14:32:53, Joe Lawrence wrote:
> >>>>> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> >>>>> index 972520144713..e01dfa3b58d2 100644
> >>>>> --- a/kernel/livepatch/core.c
> >>>>> +++ b/kernel/livepatch/core.c
> >>>>> @@ -45,7 +45,7 @@
> >>>>>   */
> >>>>>  DEFINE_MUTEX(klp_mutex);
> >>>>>  
> >>>>> -/* Registered patches */
> >>>>> +/* Actively used patches. */
> >>>>>  LIST_HEAD(klp_patches);
> >>>>
> >>>> By itself, this comment makes me wonder if there are un-active and/or
> >>>> un-used patches that I need to worry about.  After this patchset,
> >>>> klp_patches will include patches that have been enabled and those that
> >>>> have been replaced, but the replacement transition is still in progress.  
> >>>>
> >>>> If that sounds accurate, how about adding to the comment:
> >>>>
> >>>> /* Actively used patches: enabled or replaced and awaiting transition */
> >>>
> >>> The replaced patches are not in the list. This is why I used the word
> >>> "actively".
> >>
> 
> After writing out my suggestion I realized that's why you chose
> "actively" and almost erased my comment.  I think the extra text would
> help a fresh reader of the code, so ...
> 
> >> The replaced patches are removed in klp_discard_replaced_patches(), which 
> >> is called from klp_complete_transition(). Joe is right. The patches are in 
> >> the list if a transition is still in progress.
> > 
> > These are patches that are being replaced. The replaced (after the
> >  transition finishes) are not in the list.
> > 
> > By other word, Joe's text could be understand that replaced patches
> > will never get removed from the list.
> >
> > So, is the text below acceptable?
> > 
> > /*
> >  * Actively used patches: enabled or in transition. Note that replaced
> >  * or disabled patches are not listed even though the related kernel
> >  * module still can be loaded.
> >  */
> 
> Yes this works and is more accurate than my original suggestion.

>From my perspective, no comment is needed at all, and _any_ comment just
serves to add confusion -- including the above one.  But maybe that's
because I already know that disabled and replace patches get discarded.

-- 
Josh