linux-kernel - Re: [PATCH 4/4] livepatch: Remove the redundant enabled flag in struct klp

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Message-ID: <20190130094405.qbm7nynam3dryq4h@pathway.suse.cz>
Date:   Wed, 30 Jan 2019 10:44:05 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Joe Lawrence <joe.lawrence@...hat.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 4/4] livepatch: Remove the redundant enabled flag in
 struct klp_patch

On Tue 2019-01-29 14:00:49, Josh Poimboeuf wrote:
> On Wed, Jan 23, 2019 at 01:27:59PM -0500, Joe Lawrence wrote:
> > > I wanted to ask why there is list_empty() and not klp_patch_enabled(), so
> > > just to be sure... the patch was added to klp_patches list, so patch->list
> > > is not empty (should not be). We could achieve the same by calling
> > > !klp_patch_enabled() given its implementation, but it would look
> > > counter-intuitive here.
> > > 
> > > The rest looks fine.
> > > 
> > > However, I am not sure if the outcome is better than what we have. Yes,
> > > patch->enabled is not technically necessary and we can live with that (as
> > > the patch proves). On the other hand, it gives the reader clear guidance
> > > about the patch's state. klp_patch_enabled() is not a complete
> > > replacement. We have to call list_empty() in __klp_enable_patch() or check
> > > the original klp_target_state in klp_try_complete_transition().
> > > 
> > > I am not against the change, I am glad to see it is achievable, but I am
> > > not sure if the code is better with it. Joe acked it. What do the others
> > > think?
> > 
> > Let me qualify my ack -- I think minimizing the number of state variables
> > like patch->enabled can help readability... on the other hand, deducing the
> > same information from other properties like list-empty can be confusing, ie,
> > klp_patch_enabled() is generally a lot clearer than
> > list_empty(&patch->list)).
> > 
> > So I like this idea and would be interested to hear what folks think about
> > the exception cases you pointed out.
> 
> I share Miroslav and Joe's ambivalence.  It's interesting to see that it
> can be done, and normally I'd prefer to get rid of extraneous data
> fields, but the patch doesn't reduce code, and it even makes the code
> slightly more complex IMO, because klp_patch_enabled() doesn't always
> work like you'd expect.
> 
> So while I suggested it to begin with, I'm going to go with a NACK :-)

Fair enough. I took this patch as an experiment that might fail :-)

Best Regards,
Petr