linux-kernel - Re: [PATCH 1/2] locking/lockdep: Add support for dynamic depmaps and keys

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Date:   Mon, 19 Nov 2018 13:55:06 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...hat.com, linux-kernel@...r.kernel.org,
        Will Deacon <will.deacon@....com>, Tejun Heo <tj@...nel.org>,
        Johannes Berg <johannes.berg@...el.com>
Subject: Re: [PATCH 1/2] locking/lockdep: Add support for dynamic depmaps
 and keys

On Sat, 2018-11-10 at 14:55 +0100, Peter Zijlstra wrote:
> On Fri, Nov 09, 2018 at 03:46:44PM -0800, Bart Van Assche wrote:
> > The lock validator forces to categorize multiple instances of a lock object
> > as the same lock class because it requires that struct lockdep_map and struct
> > lock_class_key instances are static objects. This can result in false
> > positive lockdep reports that are hard to suppress in an elegant way. Hence
> > add support for allocating instances of these objects dynamically.
> 
> Yeah, I think not. You completely fail to explain how what you propose
> is correct.
> 
> The thing is; we rely on static objects because they provide
> persistence. Their address will never be re-used.
> 
> Dynamic objects do not provide this same guarantee. And when you re-use
> the key address for something else, you'll mix the chains and things
> come unstuck.

Hi Peter,

Thanks for having taken a look. I will rework this patch taking your feedback
into account and will post the new version when it's ready.

Bart.