From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752237AbcEVJip (ORCPT <rfc822;w@1wt.eu>);
	Sun, 22 May 2016 05:38:45 -0400
Received: from merlin.infradead.org ([205.233.59.134]:41292 "EHLO
	merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1752088AbcEVJin (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Sun, 22 May 2016 05:38:43 -0400
Date: Sun, 22 May 2016 11:38:28 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Manfred Spraul <manfred@colorfullife.com>
Cc: Boqun Feng <boqun.feng@gmail.com>, Davidlohr Bueso <dave@stgolabs.net>,
        Waiman.Long@hpe.com, mingo@kernel.org, torvalds@linux-foundation.org,
        ggherdovich@suse.com, mgorman@techsingularity.net,
        linux-kernel@vger.kernel.org,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Will Deacon <will.deacon@arm.com>
Subject: Re: sem_lock() vs qspinlocks
Message-ID: <20160522093828.GM3193@twins.programming.kicks-ass.net>
References: <20160520053926.GC31084@linux-uzut.site>
 <20160520115819.GF3193@twins.programming.kicks-ass.net>
 <20160520140533.GA20726@insomnia>
 <20160520152149.GH3193@twins.programming.kicks-ass.net>
 <20160520160436.GQ3205@twins.programming.kicks-ass.net>
 <48cb5e2c-f346-d702-30af-2a6666886df4@colorfullife.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <48cb5e2c-f346-d702-30af-2a6666886df4@colorfullife.com>
User-Agent: Mutt/1.5.21 (2012-12-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Sun, May 22, 2016 at 10:43:08AM +0200, Manfred Spraul wrote:
> How would we handle mixed spin_lock()/mutex_lock() code?
> For the IPC code, I would like to replace the outer lock with a mutex.
> The code only uses spinlocks, because at the time it was written, the mutex
> code didn't contain a busy wait.
> With a mutex, the code would become simpler (all the
> lock/unlock/kmalloc/relock parts could be removed).
> 
> The result would be something like:
> 
> 	mutex_lock(A)			spin_lock(B)
> 	spin_unlock_wait(B)		if (!mutex_is_locked(A))
> 	do_something()			  do_something()
> 

Should work similarly, but we'll have to audit mutex for these same
issues. I'll put it on todo.