linux-kernel - Re: [PATCH] llist: Fix missing lockless

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Message-ID: <20150208005941.GA3524@kroah.com>
Date:	Sun, 8 Feb 2015 08:59:41 +0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Michael Cree <mcree@...on.net.nz>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-alpha@...r.kernel.org, Richard Henderson <rth@...ddle.net>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	Matt Turner <mattst88@...il.com>,
	Huang Ying <ying.huang@...el.com>,
	linux-kernel@...r.kernel.org,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Pranith Kumar <bobby.prani@...il.com>, stable@...r.kernel.org
Subject: Re: [PATCH] llist: Fix missing lockless_dereference()

On Sun, Feb 08, 2015 at 01:47:29PM +1300, Michael Cree wrote:
> On Sat, Feb 07, 2015 at 10:30:44PM +0000, Mathieu Desnoyers wrote:
> > > On Fri, Feb 06, 2015 at 09:08:21PM -0500, Mathieu Desnoyers wrote:
> > > > A lockless_dereference() appears to be missing in llist_del_first().
> > > > It should only matter for Alpha in practice.
> 
> What could one anticipate to be the symptoms of such a missing
> lockless_dereference()?
> 
> The Alpha kernel is behaving pretty well provided one builds a machine
> specific kernel and UP.  When running an SMP kernel some packages
> (most notably the java runtime, but there are a few others) occasionally
> lock up in a pthread call --- could be a problem in libc rather then the
> kernel.

Hm, if only UP alpha needs to be supported, odds are we could rip a lot
of odd stuff out of the kernel that deals with memory barriers and other
nasty locking things that the Alpha requires.

Would that be ok?  Or is someone somewhere going to want to be running a
SMP kernel on Alpha in the future?

thanks,

greg k-h
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