linux-kernel - Re: linux-next: build failure after merge of the rcu tree

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Message-Id: <20170811143917.GD3730@linux.vnet.ibm.com>
Date:   Fri, 11 Aug 2017 07:39:17 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: linux-next: build failure after merge of the rcu tree

On Fri, Aug 11, 2017 at 11:14:34AM +0200, Peter Zijlstra wrote:
> On Thu, Aug 10, 2017 at 09:54:53PM -0700, Paul E. McKenney wrote:
> > On Fri, Aug 11, 2017 at 02:43:52PM +1000, Stephen Rothwell wrote:
> > 
> > Looks like I need to rebase my patch on top of a9668cd6ee28, and
> > than put an smp_mb__after_spinlock() between the lock and the unlock.
> > 
> > Peter, any objections to that approach?  Other suggestions?
> 
> Hurm.. I'll have to try and understand that comment there again it
> seems.

My reasoning is as follows:

1.	The critical section is empty, so any prior references
	would be ordered only against later critical sections.

2.	A full barrier within the critical section will order those
	prior references against later critical sections just
	as easily as would one prior to the critical section.

Does that make sense, I should I have stayed away from the keyboard
at this early hour?  ;-)

							Thanx, Paul