linux-kernel - Re: CONFIG_PROVE_RCU breaks proprietary modules (rcu_lock

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Date:	Mon, 29 Mar 2010 08:09:46 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Tilman Schmidt <tilman@...p.cc>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: CONFIG_PROVE_RCU breaks proprietary modules (rcu_lock_map)

On Sun, Mar 21, 2010 at 10:04:42PM +0100, Tilman Schmidt wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> I know there's not much sympathy for troubles with proprietary modules
> here, but the following might save some trouble to kernel developers as
> well as users forced to resort to proprietary drivers:
> 
> Setting the kernel configuration option PROVE_RCU creates a reference to
> the GPL-exported global variable rcu_lock_map even in modules that do
> not use RCU. In the case of non-GPL modules, this leads to a build
> failure because of the license incompatibility.
> (I did not find out where that reference comes from.)
> 
> So if building a proprietary module fails with the message:
> 
> FATAL: modpost: GPL-incompatible module <module> uses GPL-only symbol
> 'rcu_lock_map'
> 
> try rebuilding your kernel with the PROVE_RCU option disabled.
> 
> Hope it helps someone.

I am comfortable with PROVE_RCU being incompatible with non-GPL modules.
After all, it is only a debugging option, not intended for production use.

							Thanx, Paul
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