linux-kernel - Re: [RFC 3/3] mutex: When there is no owner, stop spinning after too many tries

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Message-ID: <CA+55aFwszXHtjOW53eBLV4aMD-cv0dg7xyBa0BtN1LS4XajwLw@mail.gmail.com>
Date:	Thu, 16 Jan 2014 10:14:33 +0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Jason Low <jason.low2@...com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Waiman Long <Waiman.Long@...com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Davidlohr Bueso <davidlohr@...com>,
	Peter Anvin <hpa@...or.com>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>
Subject: Re: [RFC 3/3] mutex: When there is no owner, stop spinning after too
 many tries

On Thu, Jan 16, 2014 at 9:45 AM, Jason Low <jason.low2@...com> wrote:
>
> Any comments on the below change which unlocks the mutex before taking
> the lock->wait_lock to wake up a waiter? Thanks.

Hmm. Doesn't that mean that a new lock owner can come in *before*
you've called debug_mutex_unlock and the lockdep stuff, and get the
lock? And then debug_mutex_lock() will be called *before* the unlocker
called debug_mutex_unlock(), which I'm sure confuses things.

          Linus
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