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

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Date:	Fri, 4 Dec 2015 01:11:29 +0100 (CET)
From:	Jiri Kosina <jikos@...nel.org>
To:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>
cc:	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 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).

What do you think?

Thanks a lot,

-- 
Jiri Kosina
SUSE Labs

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