linux-kernel - Re: [PATCH] block: model freeze & enter queue as rwsem for supporting lockdep

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Message-ID: <20241022072112.GA12249@lst.de>
Date: Tue, 22 Oct 2024 09:21:12 +0200
From: Christoph Hellwig <hch@....de>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Christoph Hellwig <hch@....de>, Ming Lei <ming.lei@...hat.com>,
	Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
	Waiman Long <longman@...hat.com>, Boqun Feng <boqun.feng@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] block: model freeze & enter queue as rwsem for
 supporting lockdep

On Tue, Oct 22, 2024 at 09:19:05AM +0200, Peter Zijlstra wrote:
> > Not sure modelling it as a trylock is the right approach here,
> > I've added the lockdep maintainers if they have an idea.
> 
> So lockdep supports recursive reader state, but you're looking at
> recursive exclusive state?

Yes.

> If you achieve this using an external nest count, then it is probably (I
> haven't yet had morning juice) sufficient to use the regular exclusive
> state on the outermost lock / unlock pair and simply ignore the inner
> locks.

There obviosuly is an external nest count here, so I guess that should
do the job.  Ming?