linux-kernel - Re: [PATCH v2 09/17] debugobjects: Make object hash locks nestable terminal locks

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Date:   Fri, 7 Dec 2018 10:47:39 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Tejun Heo <tj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 09/17] debugobjects: Make object hash locks nestable
 terminal locks

On Mon, Nov 19, 2018 at 01:55:18PM -0500, Waiman Long wrote:
> By making the object hash locks nestable terminal locks, we can avoid
> a bunch of unnecessary lockdep validations as well as saving space
> in the lockdep tables.

So the 'problem'; which you've again not explained; is that debugobjects
has the following lock order:

	&db->lock
	  &pool_lock

And you seem to want to tag '&db->lock' as terminal, which is obviuosly
a big fat lie.

You've also not explained why it is safe to do this (I think it actually
is, but you really should've spelled it out).

Furthermore; you've not justified any of this 'insanity' with numbers.
What do we gain with this nestable madness that justifies the crazy?