linux-kernel - Re: [RFC] workqueue: remove manual lockdep uses to detect deadlocks

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Message-ID: <20170828065553.gikwc5zsuy2762eg@hirez.programming.kicks-ass.net>
Date:   Mon, 28 Aug 2017 08:55:53 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Byungchul Park <byungchul.park@....com>
Cc:     tj@...nel.org, johannes.berg@...el.com, mingo@...nel.org,
        tglx@...utronix.de, linux-kernel@...r.kernel.org,
        kernel-team@....com
Subject: Re: [RFC] workqueue: remove manual lockdep uses to detect deadlocks

On Fri, Aug 25, 2017 at 05:41:03PM +0900, Byungchul Park wrote:
> Hello all,
> 
> This is _RFC_.
> 
> I want to request for comments about if it's reasonable conceptually. If
> yes, I want to resend after working it more carefully.
> 
> Could you let me know your opinions about this?
> 
> ----->8-----
> From 448360c343477fff63df766544eec4620657a59e Mon Sep 17 00:00:00 2001
> From: Byungchul Park <byungchul.park@....com>
> Date: Fri, 25 Aug 2017 17:35:07 +0900
> Subject: [RFC] workqueue: remove manual lockdep uses to detect deadlocks
> 
> We introduced the following commit to detect deadlocks caused by
> wait_for_completion() in flush_{workqueue, work}() and other locks. But
> now LOCKDEP_COMPLETIONS is introduced, such works are automatically done
> by LOCKDEP_COMPLETIONS. So it doesn't have to be done manually anymore.
> Removed it.
> 

No.. the existing annotation is strictly better because it will _always_
warn. It doesn't need to first observe things just right.