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Date: Sun, 11 Nov 2018 02:28:23 +0100
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [RFC PATCH 01/12] locking/lockdep: Rework
 lockdep_set_novalidate_class()
Message-ID: <20181111012823.GB12766@worktop.psav.com>
References: <1541709268-3766-1-git-send-email-longman@redhat.com>
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To: Waiman Long <longman@redhat.com>
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 Sat, Nov 10, 2018 at 07:26:51PM -0500, Waiman Long wrote:
> On 11/10/2018 09:14 AM, Peter Zijlstra wrote:
> > On Thu, Nov 08, 2018 at 03:34:17PM -0500, Waiman Long wrote:
> >> The current lockdep_set_novalidate_class() implementation is like
> >> a hack. It assigns a special class key for that lock and calls
> >> lockdep_init_map() twice.
> > Ideally it would go away.. it is not thing that should be used.
> 
> Yes, I agree. Right now, lockdep_set_novalidate_class() is used in
> 
> drivers/base/core.c:    lockdep_set_novalidate_class(&dev->mutex);
> drivers/md/bcache/btree.c:      lockdep_set_novalidate_class(&b->lock);
> drivers/md/bcache/btree.c:     
> lockdep_set_novalidate_class(&b->write_lock);
> 
> Do you know the history behind making them novalidate?

Only of the driver/base/core.c one; there the locking order depends on
the hardware and we never quite found a way to annotate that sanely. I
forgot most details though.

The other stuff I only 'recently' found out about :-( And ideally would
have never made it into the tree, but alas.