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

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Message-ID: <20151204132724.GH11394@treble.redhat.com>
Date:	Fri, 4 Dec 2015 07:27:24 -0600
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Jiri Kosina <jikos@...nel.org>
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, Dec 04, 2015 at 01:11:29AM +0100, Jiri Kosina wrote:
> On Thu, 3 Dec 2015, Josh Poimboeuf wrote:
> 
> > Calling set_memory_rw() and set_memory_ro() for every iteration of the
> > loop in klp_write_object_relocations() is messy, inefficient, and
> > error-prone.
> > 
> > Change all the read-only pages to read-write before the loop and convert
> > them back to read-only again afterwards.
> > 
> > Suggested-by: Miroslav Benes <mbenes@...e.cz>
> > Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> > ---
> > Based on the following branches:
> > - git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching.git for-4.5/core
> > - git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux.git modules-next
> > 
> > - v4: rebase onto Chris's sympos changes
> > - v3: use new module_{disable,enable}_ro() functions (in linux-next)
> 
> Rusty,
> 
> how would you like to handle this cross-tree dependency?
> 
> My proposals:
> 
> (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?

-- 
Josh
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