linux-kernel - Re: [c++std-parallel-1624] Re: Compilers and RCU readers: Once more unto the breach!

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Message-ID: <20150520140216.GN6776@linux.vnet.ibm.com>
Date:	Wed, 20 May 2015 07:02:16 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	c++std-parallel@...u.org
Cc:	dhowells@...hat.com, Will Deacon <will.deacon@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"gcc@....gnu.org" <gcc@....gnu.org>,
	p796231 <Peter.Sewell@...cam.ac.uk>,
	"mark.batty@...cam.ac.uk" <Mark.Batty@...cam.ac.uk>,
	Peter Zijlstra <peterz@...radead.org>,
	Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	"michaelw@...ibm.com" <michaelw@...ibm.com>
Subject: Re: [c++std-parallel-1624] Re: Compilers and RCU readers: Once more
 unto the breach!

On Wed, May 20, 2015 at 02:37:05PM +0100, David Howells wrote:
> Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:
> 
> > I was thinking of "y" as a simple variable, but if it is something more
> > complex, then the compiler could do this, right?
> > 
> > 	char *x;
> > 
> > 	y;
> > 	x = z;
> 
> Yeah.  I presume it has to maintain the ordering, though.

Agreed.  Unless of course y writes to x or some such.

Given that there is already code in the Linux kernel relying on
dependencies being carried through stores to local variables,
this should not be a problem.

Or am I missing something?

							Thanx, Paul

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