linux-kernel - Re: [PATCH] Documentation/memory-barriers: fix wrong comment in example

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Date:	Mon, 22 Feb 2016 08:33:22 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	David Howells <dhowells@...hat.com>
Cc:	SeongJae Park <sj38.park@...il.com>,
	Jonathan Corbet <corbet@....net>,
	linux-doc <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Documentation/memory-barriers: fix wrong comment in
 example

On Mon, Feb 22, 2016 at 11:16:39AM +0000, David Howells wrote:
> SeongJae Park <sj38.park@...il.com> wrote:
> 
> > From f7b5677790771599f418f1d95536935be971ae86 Mon Sep 17 00:00:00 2001
> > From: SeongJae Park <sj38.park@...il.com>
> > Date: Mon, 22 Feb 2016 19:26:18 +0900
> > Subject: [PATCH] Documentation/memory-barriers: polish compiler store omit
> >  example
> > 
> > Comments of examples about compiler store omit in memory-barriers.txt is
> > about code that could be possible at that point.  However, someone could
> > interpret the comment as an explanation about below line.  This commit
> > exploits the intent more explicitly by changing the comment to be seems
> > like a possible code rather than explanation about below line.
> > 
> > Signed-off-by: SeongJae Park <sj38.park@...il.com>
> > ---
> >  Documentation/memory-barriers.txt | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/Documentation/memory-barriers.txt
> > b/Documentation/memory-barriers.txt
> > index 904ee42..dc66351 100644
> > --- a/Documentation/memory-barriers.txt
> > +++ b/Documentation/memory-barriers.txt
> > @@ -1459,7 +1459,7 @@ of optimizations:
> >       the following:
> > 
> >         a = 0;
> > -       /* Code that does not store to variable a. */
> > +       ... Code that does not store to variable a ...
> >         a = 0;
> > 
> >       The compiler sees that the value of variable 'a' is already zero, so
> > @@ -1471,7 +1471,7 @@ of optimizations:
> >       wrong guess:
> > 
> >         WRITE_ONCE(a, 0);
> > -       /* Code that does not store to variable a. */
> > +       ... Code that does not store to variable a ...
> >         WRITE_ONCE(a, 0);
> > 
> >   (*) The compiler is within its rights to reorder memory accesses unless
> 
> Acked-by: David Howells <dhowells@...hat.com>

Thank you both!  Patch with updated commit log below, please let me know
if you have any objections to the changes.

							Thanx, Paul

------------------------------------------------------------------------

commit 0a41feb6ab4da3218192e2cde1a54fcc5d8f5658
Author: SeongJae Park <sj38.park@...il.com>
Date:   Mon Feb 22 08:28:29 2016 -0800

    documentation: Clarify compiler store-fusion example
    
    The compiler store-fusion example in memory-barriers.txt uses a C
    comment to represent arbitrary code that does not update a given
    variable.  Unfortunately, someone could reasonably interpret the
    comment as instead referring to the following line of code.  This
    commit therefore replaces the comment with a string that more
    clearly represents the arbitrary code.
    
    Signed-off-by: SeongJae Park <sj38.park@...il.com>
    Acked-by: David Howells <dhowells@...hat.com>
    Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index 8367d393cba2..3729cbe60e41 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -1550,7 +1550,7 @@ of optimizations:
      the following:
 
 	a = 0;
-	/* Code that does not store to variable a. */
+	... Code that does not store to variable a ...
 	a = 0;
 
      The compiler sees that the value of variable 'a' is already zero, so
@@ -1562,7 +1562,7 @@ of optimizations:
      wrong guess:
 
 	WRITE_ONCE(a, 0);
-	/* Code that does not store to variable a. */
+	... Code that does not store to variable a ...
 	WRITE_ONCE(a, 0);
 
  (*) The compiler is within its rights to reorder memory accesses unless