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

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Message-ID: <20181110135524.GC3339@worktop.programming.kicks-ass.net>
Date:   Sat, 10 Nov 2018 14:55:24 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Bart Van Assche <bvanassche@....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 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.