linux-kernel - Re: [RFC] locking/rwsem: Avoid issuing wakeup before setting the reader waiter to nil

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Message-ID: <20181129181715.dqqv6apsv4p47rry@linux-r8p5>
Date:   Thu, 29 Nov 2018 10:17:16 -0800
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Waiman Long <longman@...hat.com>, Yongji Xie <elohimes@...il.com>,
        mingo@...hat.com, will.deacon@....com,
        linux-kernel@...r.kernel.org, xieyongji@...du.com,
        zhangyu31@...du.com, liuqi16@...du.com, yuanlinsi01@...du.com,
        nixun@...du.com, lilin24@...du.com
Subject: Re: [RFC] locking/rwsem: Avoid issuing wakeup before setting the
 reader waiter to nil

On Thu, 29 Nov 2018, Peter Zijlstra wrote:

>On Thu, Nov 29, 2018 at 12:58:26PM -0500, Waiman Long wrote:
>> OK, you convinced me. However, that can still lead to anonymous wakeups
>> that can be problematic if it happens in certain places. Should we try
>> to reduce anonymous wakeup as much as possible?
>
>No, we should at all times accept and expect spurious wakeups.

Right, when this was merged, spurious wakeups were acknowledged as quite
possible.