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Subject: Re: [RFC PATCH 07/12] locking/lockdep: Add support for nested
 terminal locks
References: <1541709268-3766-1-git-send-email-longman@redhat.com>
 <1541709268-3766-8-git-send-email-longman@redhat.com>
 <20181110142023.GG3339@worktop.programming.kicks-ass.net>
From: Waiman Long <longman@redhat.com>
Message-ID: <f3fc6819-175b-6452-4705-942a82d7e06f@redhat.com>
Date: Sat, 10 Nov 2018 19:30:54 -0500
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To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>, Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, linux-mm@kvack.org, Petr Mladek <pmladek@suse.com>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, Andrey Ryabinin <aryabinin@virtuozzo.com>, Tejun Heo <tj@kernel.org>, Andrew Morton <akpm@linux-foundation.org>

On 11/10/2018 09:20 AM, Peter Zijlstra wrote:
> On Thu, Nov 08, 2018 at 03:34:23PM -0500, Waiman Long wrote:
>> There are use cases where we want to allow 2-level nesting of one
>> terminal lock underneath another one. So the terminal lock type is now
>> extended to support a new nested terminal lock where it can allow the
>> acquisition of another regular terminal lock underneath it.
> You're stretching things here... If you're allowing things under it, it
> is no longer a terminal lock.
>
> Why would you want to do such a thing?

A majority of the gain in debugobjects is to make the hash lock a kind
of terminal lock. Yes, I may be stretching it a bit here. I will take
back the nesting patch and consider doing that in a future patch.

Cheers,
Longman