linux-kernel - Re: [PATCH] livepatch: add module locking around kallsyms calls

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Message-ID: <alpine.LNX.2.00.1506022255310.12753@pobox.suse.cz>
Date:	Tue, 2 Jun 2015 22:58:42 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Miroslav Benes <mbenes@...e.cz>
cc:	sjenning@...hat.com, Vojtech Pavlik <vojtech@...e.cz>,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
	pmladek@...e.cz
Subject: Re: [PATCH] livepatch: add module locking around kallsyms calls

On Tue, 2 Jun 2015, Josh Poimboeuf wrote:

> On Mon, Jun 01, 2015 at 05:48:37PM +0200, Miroslav Benes wrote:
> > The list of loaded modules is walked through in
> > module_kallsyms_on_each_symbol (called by kallsyms_on_each_symbol). The
> > module_mutex lock should be acquired to prevent potential corruptions
> > in the list.
> > 
> > This was uncovered with new lockdep asserts in module code introduced by
> > the commit 0be964be0d45 ("module: Sanitize RCU usage and locking") in
> > recent next- trees.
> > 
> > Signed-off-by: Miroslav Benes <mbenes@...e.cz>
> 
> Thanks!
> 
> Should we add a comment to kallsyms_on_each_symbol() so that others
> don't make this mistake?

Yeah, the locking rules in module loader are not really crystal clear (not 
even after Peterz's revamp in -next), so some comment / lockdep assertion 
might be helpful. But let's keep that separate from this functional fix in 
klp.

> Acked-by: Josh Poimboeuf <jpoimboe@...hat.com>

I have now queued this in for-4.1/upstream-fixes, but I don't think I'll 
rush this in for -final now, therefore I added Cc: stable as well. If 
there is -rc7, I'll push it to Linus for -final early next week.

Thanks,

-- 
Jiri Kosina
SUSE Labs
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