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

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Message-ID: <20181214100232.elyqlnjyhp55acxf@pathway.suse.cz>
Date:   Fri, 14 Dec 2018 11:02:32 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Jiri Kosina <jikos@...nel.org>, Miroslav Benes <mbenes@...e.cz>,
        Jason Baron <jbaron@...mai.com>,
        Joe Lawrence <joe.lawrence@...hat.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 2018-12-13 16:46:25, Josh Poimboeuf wrote:
> Now that we can't re-enable a patch, I wonder if we really need both the
> 'patch->enabled' and 'klp_target_state' variables?
> 
> A patch is now always enabled, unless it's in transition, in which case
> its 'enabled' state is the same as 'klp_target_state'.
>
> For example I wonder if we could get rid of 'klp_target_state', since it
> should be the same as 'klp_transition_patch->enabled'.

There are some catches:

1. klp_update_patch_state() can be called anywhere and anytime. We
   would add yet another race-sensitive code if we access the flag
   via a pointer.

2. patch->enabled is bool while klp_target_state is triple state.
   The argument is that KLP_UNDEFINED helps to catch bugs.


> Or alternatively we could get rid of 'patch->enabled', since it should
> be the same as
> 
> 	patch == klp_transition_patch ? klp_target_state : true

This might solve the first catch but not the 2nd one. Not to say
that it is much harder to read.


> Of course this could be a follow-on cleanup patch, which could be done
> in the future, so as not to hold up the merging of these patches
> anymore.

Yes, please. This is controversial, non-trivial, and can wait.

Best Regards,
Petr