linux-kernel - Re: [locking/lockdep] 383776fa75: INFO: trying to register non-static key.

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Date:   Fri, 17 Mar 2017 15:41:41 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     kernel test robot <fengguang.wu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>, LKP <lkp@...org>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>, wfg@...ux.intel.com
Subject: Re: [locking/lockdep] 383776fa75:  INFO: trying to register
 non-static key.

On 2017-03-17 14:41:09 [+0100], Peter Zijlstra wrote:
> On Fri, Mar 17, 2017 at 02:07:05AM +0800, kernel test robot wrote:
> 
> >     locking/lockdep: Handle statically initialized PER_CPU locks properly
> 
> > [   11.712266] INFO: trying to register non-static key.
> 
> Blergh; so the problem is that when we assign can_addr to lock->key, we
> can, upon using a different subclass, reach static_obj(lock->key), which
> will fail on the can_addr.
> 
> One way to fix this would be to redefine the canonical address as the
> per-cpu address for a specific cpu; the below hard codes cpu0, but I'm
> not sure we want to rely on cpu0 being a valid cpu.

This solves two problems: The one reported by the bot. The other thing,
that is fixed by the patch, is that the first PER-CPU variable built-in
will return 0 for can_addr and so will the first variable in every
module. As far as I understand it, this should be unique and having the
same value for multiple different variables does not look too good :)
So adding the offset from CPU0 sounds good.

Sebastian