linux-kernel - Re: using long instead of atomic_t when only set/read is required (was Re: [Bug 10030] Suspend doesn't work when SD card is inserted)

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Message-ID: <Pine.LNX.4.44L0.0802250943410.3549-100000@iolanthe.rowland.org>
Date:	Mon, 25 Feb 2008 09:46:06 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Pavel Machek <pavel@....cz>
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: Re: using long instead of atomic_t when only set/read is required
 (was Re: [Bug 10030] Suspend doesn't work when SD card is inserted)

On Mon, 25 Feb 2008, Pavel Machek wrote:

> 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.

> I guess it only works as long as longs are aligned? Should it be
> written down to atomic_ops.txt?

Forget it, I'm going to withdraw the entire thing.  The whole approach 
is wrong.  More details in a new email thread, to follow soon.

Alan Stern

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