linux-kernel - Re: [PATCH v4 08/16] locking/rwsem: Make rwsem_spin_on

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Message-ID: <20190417101903.GD4038@hirez.programming.kicks-ass.net>
Date:   Wed, 17 Apr 2019 12:19:03 +0200
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, x86@...nel.org,
        Davidlohr Bueso <dave@...olabs.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        huang ying <huang.ying.caritas@...il.com>
Subject: Re: [PATCH v4 08/16] locking/rwsem: Make rwsem_spin_on_owner()
 return owner state

On Sat, Apr 13, 2019 at 01:22:51PM -0400, Waiman Long wrote:
> In the special case that there is no active lock and the handoff bit
> is set, optimistic spinning has to be stopped.

This makes me think this should've been _before_ you added the handoff
bit. So that when you introduce the handoff, everything is solid.