linux-kernel - Re: [PATCH tip/core/rcu 2/3] documentation: Update rcu_dereference.txt based on WG21 discussions

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Message-ID: <20150514205750.GH6776@linux.vnet.ibm.com>
Date:	Thu, 14 May 2015 13:57:51 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, josh@...htriplett.org,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
	dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
	fweisbec@...il.com, oleg@...hat.com,
	bobby prani <bobby.prani@...il.com>
Subject: Re: [PATCH tip/core/rcu 2/3] documentation: Update
 rcu_dereference.txt based on WG21 discussions

On Wed, May 13, 2015 at 06:33:10PM +0000, Mathieu Desnoyers wrote:
> ----- Original Message -----
> > From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> > 
> > This commit provides another caveat for the care and feeding of pointers
> > returned by rcu_dereference() that was pointed out in discussions within
> > the C++ standards committee.
> > 
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> 
> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

Thank you, applied.

> BTW, reading through rcu_dereference.txt, I found a nit:
> 
> operatiors -> operators

Hmmm...  Almost like I was trying (and spectacularly failing) to write
the document in French.  ;-)

> Very interesting reading :)

Glad you liked it!

							Thanx, Paul

> Thanks!
> 
> Mathieu
> 
> > ---
> >  Documentation/RCU/rcu_dereference.txt | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/Documentation/RCU/rcu_dereference.txt
> > b/Documentation/RCU/rcu_dereference.txt
> > index ceb05da5a5ac..2d05c9241a33 100644
> > --- a/Documentation/RCU/rcu_dereference.txt
> > +++ b/Documentation/RCU/rcu_dereference.txt
> > @@ -193,6 +193,11 @@ o	Be very careful about comparing pointers obtained from
> >  		pointer.  Note that the volatile cast in rcu_dereference()
> >  		will normally prevent the compiler from knowing too much.
> >  
> > +		However, please note that if the compiler knows that the
> > +		pointer takes on only one of two values, a not-equal
> > +		comparison will provide exactly the information that the
> > +		compiler needs to deduce the value of the pointer.
> > +
> >  o	Disable any value-speculation optimizations that your compiler
> >  	might provide, especially if you are making use of feedback-based
> >  	optimizations that take data collected from prior runs.  Such
> > --
> > 1.8.1.5
> > 
> > 
> 
> -- 
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com
> 

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