From: Linus Torvalds <torvalds@linux-foundation.org>
To: Mark Lord <lkml@rtr.ca>
Cc: Alan Stern <stern@rowland.harvard.edu>,
Alan Cox <alan@lxorguk.ukuu.org.uk>, Pavel Machek <pavel@ucw.cz>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
Zdenek Kabelac <zdenek.kabelac@gmail.com>,
davem@davemloft.net, "Rafael J. Wysocki" <rjw@sisk.pl>,
Pierre Ossman <drzeus-mmc@drzeus.cx>,
Kernel development list <linux-kernel@vger.kernel.org>,
pm list <linux-pm@lists.linux-foundation.org>
Subject: Re: [patch] Re: using long instead of atomic_t when only set/read is required
Date: Thu, 6 Mar 2008 08:11:59 -0800 (PST) [thread overview]
Message-ID: <alpine.LFD.1.00.0803060807120.12253@woody.linux-foundation.org> (raw)
In-Reply-To: <47D014A6.9090300@rtr.ca>
On Thu, 6 Mar 2008, Mark Lord wrote:
>
> But also consider something like this:
>
> void store_task(void)
> {
> *the_task = current;
> }
>
> In this case, there is no guarantee that the assignment
> can be done atomically on all CPU types. Some RISC archs
> (eg. MIPS R2xxx) require an (interruptible) instruction pair
> to store values to a potentially unaligned address.
You'd better not be using unaligned accesses for memory-ordering-sensitive
things (I think x86 happens get even that right for most cases, but I
don't think the architecture specification guarantees it, and I'm pretty
sure that you might find problems on cache crossing writes, for example)
But quite frankly, if you have an architecture that can't do the above as
a single write when it's a pointer, then you have a totally broken
architecture. It's not worth supporting.
(There are data structures that are harder than native words: bytes and
shorts can require load-modify-write cycles, and "u64" and friends can
obviously be multiple words, so you shouldn't depend on things for those
"complex" cases. But we *definitely* depend on atomicity for regular word
accesses).
Linus
next prev parent reply other threads:[~2008-03-06 16:13 UTC|newest]
Thread overview: 93+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20080219232338.E9A24108068@picon.linux-foundation.org>
2008-02-20 16:42 ` [Bug 10030] Suspend doesn't work when SD card is inserted Alan Stern
2008-02-20 17:30 ` Pierre Ossman
2008-02-20 19:26 ` Alan Stern
2008-02-20 20:51 ` Pierre Ossman
2008-02-20 20:58 ` Rafael J. Wysocki
2008-02-20 21:06 ` Alan Stern
2008-02-20 22:15 ` Rafael J. Wysocki
2008-02-20 22:24 ` Alan Stern
2008-02-20 22:41 ` Rafael J. Wysocki
2008-02-21 0:02 ` Rafael J. Wysocki
2008-02-21 16:27 ` Alan Stern
2008-02-21 16:38 ` Rafael J. Wysocki
2008-02-21 17:48 ` Alan Stern
2008-02-21 22:47 ` Rafael J. Wysocki
2008-02-21 23:05 ` Alan Stern
2008-02-23 1:30 ` Rafael J. Wysocki
2008-02-23 4:39 ` Alan Stern
2008-02-23 20:16 ` Rafael J. Wysocki
2008-02-23 23:29 ` Alan Stern
2008-02-24 0:19 ` Rafael J. Wysocki
2008-02-24 3:25 ` Alan Stern
2008-02-24 4:26 ` [linux-pm] " Alan Stern
2008-02-24 14:00 ` Rafael J. Wysocki
2008-02-24 15:33 ` Bugs in MMC [was: [Bug 10030] Suspend doesn't work when SD card is inserted] Alan Stern
2008-02-25 17:41 ` Pierre Ossman
2008-02-25 17:58 ` Alan Stern
2008-02-25 18:31 ` Pierre Ossman
2008-02-25 20:00 ` Alan Stern
2008-03-01 14:11 ` Pierre Ossman
2008-03-01 14:36 ` Alan Stern
2008-03-01 14:47 ` Pierre Ossman
2008-02-25 22:51 ` Felipe Balbi
2008-03-03 21:59 ` David Brownell
2008-03-04 6:03 ` Pierre Ossman
2008-03-04 9:44 ` David Brownell
2008-03-04 9:58 ` Pierre Ossman
2008-03-06 21:23 ` David Brownell
2008-03-04 17:53 ` Alan Stern
2008-03-04 18:53 ` David Brownell
2008-03-04 19:51 ` Alan Stern
2008-03-04 20:30 ` David Brownell
2008-03-04 21:00 ` Alan Stern
2008-03-06 15:55 ` Pavel Machek
2008-03-06 20:33 ` Alan Stern
2008-03-06 20:53 ` Zdenek Kabelac
2008-03-06 21:31 ` Rafael J. Wysocki
2008-03-04 17:50 ` Alan Stern
2008-02-24 13:33 ` [Bug 10030] Suspend doesn't work when SD card is inserted Rafael J. Wysocki
2008-02-24 20:25 ` Rafael J. Wysocki
2008-02-24 20:45 ` Alan Stern
2008-02-24 20:56 ` Rafael J. Wysocki
2008-02-24 21:11 ` Alan Stern
2008-02-24 22:18 ` Rafael J. Wysocki
2008-02-24 13:51 ` Rafael J. Wysocki
2008-02-24 19:27 ` Alan Stern
2008-02-24 19:42 ` Zdenek Kabelac
2008-02-24 20:09 ` Rafael J. Wysocki
2008-02-24 18:21 ` Pavel Machek
2008-02-24 19:03 ` Alan Stern
2008-02-24 20:11 ` Pavel Machek
2008-02-24 20:33 ` Alan Stern
2008-02-24 21:42 ` Pavel Machek
2008-02-24 22:21 ` Rafael J. Wysocki
2008-02-25 2:21 ` Alan Stern
2008-02-25 11:41 ` Rafael J. Wysocki
[not found] ` <c4e36d110802250402q7312a488idf752e07db7504e8@mail.gmail.com>
2008-02-25 12:31 ` Rafael J. Wysocki
2008-02-25 2:19 ` Alan Stern
2008-02-25 9:03 ` 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) Pavel Machek
2008-02-25 14:46 ` Alan Stern
2008-03-03 12:08 ` [patch] Re: using long instead of atomic_t when only set/read is required Pavel Machek
2008-03-03 15:42 ` Alan Stern
2008-03-03 15:53 ` Alan Cox
2008-03-03 17:11 ` Alan Stern
2008-03-03 17:26 ` Linus Torvalds
2008-03-03 17:44 ` Pavel Machek
2008-03-03 19:27 ` Alan Stern
2008-03-06 15:58 ` Mark Lord
2008-03-06 16:11 ` Linus Torvalds [this message]
2008-03-06 16:27 ` Mark Lord
2008-03-03 17:16 ` Nick Piggin
2008-03-03 17:31 ` Paul E. McKenney
2008-03-03 17:33 ` Alan Cox
2008-03-03 17:22 ` Paul E. McKenney
2008-03-03 15:48 ` Alan Cox
2008-03-03 17:24 ` Pavel Machek
2008-03-03 20:27 ` Rafael J. Wysocki
2008-03-03 21:12 ` Paul E. McKenney
2008-03-03 22:23 ` Linus Torvalds
2008-03-04 23:32 ` Peter Hartley
2008-03-04 23:54 ` Rafael J. Wysocki
2008-03-05 0:26 ` Paul E. McKenney
2008-02-25 11:40 ` [Bug 10030] Suspend doesn't work when SD card is inserted Rafael J. Wysocki
2008-03-05 17:07 [patch] Re: using long instead of atomic_t when only set/read is required Matti Linnanvuori
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