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

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Date:   Thu, 6 Dec 2018 09:36:06 -0500
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Petr Mladek <pmladek@...e.com>, Miroslav Benes <mbenes@...e.cz>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        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 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.

Thanks,

-- Joe