linux-kernel - [patch] Re: using long instead of atomic

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Date:	Mon, 3 Mar 2008 13:08:42 +0100
From:	Pavel Machek <pavel@....cz>
To:	Alan Stern <stern@...land.harvard.edu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...l.org>
Cc:	Zdenek Kabelac <zdenek.kabelac@...il.com>, davem@...emloft.net,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Pierre Ossman <drzeus-mmc@...eus.cx>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: [patch] Re: using long instead of atomic_t when only set/read is
	required

Hi!

> > Alan thinks that `subj` is correct...
> 
> More precisely, reads and writes of pointers are always atomic.  That 
> is, if a write and a read occur concurrently, it is guaranteed that the 
> read will obtain either the old or the new value of the pointer, never 
> a mish-mash of the two.  If this were not so then RCU wouldn't work.

Ok, so linux actually atomicity of long?

If so, this should probably be applied...

Signed-off-by: Pavel Machek <pavel@...e.cz>

diff --git a/Documentation/atomic_ops.txt b/Documentation/atomic_ops.txt
index 4ef2450..0a7d180 100644
--- a/Documentation/atomic_ops.txt
+++ b/Documentation/atomic_ops.txt
@@ -21,6 +21,9 @@ local_t is very similar to atomic_t. If 
 updated by one CPU, local_t is probably more appropriate. Please see
 Documentation/local_ops.txt for the semantics of local_t.
 
+long (and int and void *) can be used instead of atomic_t, if all you
+need is atomic setting and atomic reading.
+
 The first operations to implement for atomic_t's are the initializers and
 plain reads.
 



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