Re: [PATCH tip/core/rcu 2/3] documentation: Update rcu_dereference.txt based on WG21 discussions
From: Paul E. McKenney
Date: Thu May 14 2015 - 16:58:04 EST
On Wed, May 13, 2015 at 06:33:10PM +0000, Mathieu Desnoyers wrote:
> ----- Original Message -----
> > From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
> > 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@xxxxxxxxxxxxxxxxxx>
> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
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!
> > ---
> > 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
> > --
> > 126.96.36.199
> Mathieu Desnoyers
> EfficiOS Inc.
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