linux-kernel - Re: [PATCH v4] locking/rwsem: Make handoff bit handling more consistent

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Message-ID: <20211115230728.GS174703@worktop.programming.kicks-ass.net>
Date:   Tue, 16 Nov 2021 00:07:28 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        linux-kernel@...r.kernel.org, Davidlohr Bueso <dave@...olabs.net>,
        mazhenhua <mazhenhua@...omi.com>,
        Hillf Danton <hdanton@...a.com>,
        Maria Yu <quic_aiquny@...cinc.com>
Subject: Re: [PATCH v4] locking/rwsem: Make handoff bit handling more
 consistent

On Mon, Nov 15, 2021 at 05:29:10PM -0500, Waiman Long wrote:
> 
> The handoff_set flag can only be true for a first waiter. A random waiter in
> the middle of a wait queue will never has this flag set.
> 
> This flag is set in two places in rwsem_try_write_lock():

Bah, I thought it would unconditionally propagate the bit from @count. I
missed the early exit :/