linux-kernel - Re: [PATCH] locking/mutex: Set and clear owner using WRITE

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Date:	Sat, 21 May 2016 00:09:30 -0400
From:	Waiman Long <waiman.long@....com>
To:	Davidlohr Bueso <dave@...olabs.net>
CC:	Jason Low <jason.low2@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Terry Rudd <terry.rudd@....com>,
	Scott J Norton <scott.norton@....com>,
	Jason Low <jason.low2@...com>
Subject: Re: [PATCH] locking/mutex: Set and clear owner using WRITE_ONCE()

On 05/20/2016 09:00 PM, Davidlohr Bueso wrote:
> On Fri, 20 May 2016, Waiman Long wrote:
>
>> I think mutex-debug.h also needs similar changes for completeness.
>
> Maybe, but given that with debug the wait_lock is unavoidable, doesn't
> this send the wrong message?
>
> Thanks,
> Davidlohr

You are right. Optimistic spinning is disabled when DEBUG_MUTEXES is 
true. So WRITE_ONCE() is not really needed. However, I think we should 
have at least a comment in mutex-debug.h as to why the owner field is 
handled differently from mutex.h.

Cheers,
Longman