linux-kernel - Re: [PATCH v4] livepatch: Cleanup module page permission changes

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Date:	Fri, 4 Dec 2015 22:57:45 +0100 (CET)
From:	Jiri Kosina <jikos@...nel.org>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Seth Jennings <sjenning@...hat.com>,
	Vojtech Pavlik <vojtech@...e.com>,
	linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
	Miroslav Benes <mbenes@...e.cz>
Subject: Re: [PATCH v4] livepatch: Cleanup module page permission changes

On Fri, 4 Dec 2015, Josh Poimboeuf wrote:

> > (1) I pull your 'modules-next' branch, apply this patch on top, and wait 
> >     for your merge with Linus and send merge request afterwards
> > (2) If you are okay with rebasing your tree (seems like this is 
> >     ocassionally happening), how about you prepare a branch that'd have 
> >     just b3212ec77 ("module: keep percpu symbols in module's symtab") on 
> >     top of some common base, I merge it, and the cross-dependency is gone
> > (3) I cherry-pick b3212ec77 ("module: keep percpu symbols in 
> >     module's symtab") from your tree, and apply this on top. git will 
> >     handle duplicate commits when Linus merges both just fine
> > (4) I sign this patch off and you merge it
> > 
> > (4) seems really outside the regular process. (1) is really tricky wrt. 
> > coordination of timing during the merge window. I'd prefer (2) (more 
> > git-ish way of doing things, but would require you rebasing your tree) or 
> > eventually (3) (git will handle this with grace).
> 
> [ off-list ]

:-)

> Quick question.  Just curious, because I'm new at this...
> 
> My impression was that #1 was standard operating procedure.  Merge a
> (non-rebasable) modules branch into livepatch, and then make sure to
> submit the livepatch pull request after Rusty sends his, with a note in
> the mail to Linus stating the dependency.  That seems pretty
> straightforward to me.  Or am I missing something?

It's one of the options, yes. The only drawback is that it introduces, in 
addition to the actual code cross-dependency, also maintainer timing 
cross-dependency, and it might easily go wrong during merge window. But 
I've done this quite a few times already, and it was rather smooth.

What I actually prefer doing in this case is have a common merge base as a 
separate branch that gets merged to both trees, and then it's not really 
important who merges first. But that'd require in-advance planning and 
structuring Rusty's tree for that, and that's probably not worth the 
hassle for these few patches.

Thanks,

-- 
Jiri Kosina
SUSE Labs

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