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From: Linus Torvalds <torvalds@linux-foundation.org>
To: paulmck@linux.vnet.ibm.com
Cc: Torvald Riegel <triegel@redhat.com>, Jan Kara <jack@suse.cz>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-ia64@vger.kernel.org, dsterba@suse.cz, ptesarik@suse.cz,
	rguenther@suse.de, gcc@gcc.gnu.org
Subject: Re: Memory corruption due to word sharing
Date: Wed, 1 Feb 2012 15:11:00 -0800	[thread overview]
Message-ID: <CA+55aFyzYO0CMZOgdrVV0PdG2DkbwTQG7eE7N3bp=0tQmruFEQ@mail.gmail.com> (raw)
In-Reply-To: <20120201224554.GK2382@linux.vnet.ibm.com>

On Wed, Feb 1, 2012 at 2:45 PM, Paul E. McKenney
<paulmck@linux.vnet.ibm.com> wrote:
>
> My (perhaps forlorn and naive) hope is that C++11 memory_order_relaxed
> will eventually allow ACCESS_ONCE() to be upgraded so that (for example)
> access-once increments can generate a single increment-memory instruction
> on x86.

I don't think that is a semantic issue.

gcc could do it *today* with volatile accesses. It doesn't, because
volatiles are scary and basically disables a lot of optimizations. Why
would memory ordering be substantially different just because it has a
different name?

> New architectures might eventually might define things like atomic_inc()
> in terms of C++11 atomics, but let's start with the straightforward stuff
> as and if it makes sense.

SMP-atomic or percpu atomic? Or both?

We need both variants in the kernel. If the compiler generates one of
them for us, that doesn't really much help.

                          Linus

  reply	other threads:[~2012-02-01 23:11 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-02-01 15:19 Memory corruption due to word sharing Jan Kara
2012-02-01 15:34 ` Markus Trippelsdorf
2012-02-01 16:37 ` Colin Walters
2012-02-01 16:56   ` Linus Torvalds
2012-02-01 17:11     ` Jiri Kosina
2012-02-01 17:37       ` Linus Torvalds
2012-02-01 17:41       ` Michael Matz
2012-02-01 18:09         ` David Miller
2012-02-01 18:45           ` Jeff Law
2012-02-01 19:09             ` Linus Torvalds
2012-02-02 15:51               ` Jeff Garzik
2012-02-01 18:57           ` Linus Torvalds
2012-02-01 19:04           ` Peter Bergner
2012-02-01 18:52         ` Linus Torvalds
2012-02-02  9:35           ` Richard Guenther
2012-02-02  9:37           ` Richard Guenther
2012-02-02 13:43           ` Michael Matz
2012-02-01 16:41 ` Linus Torvalds
2012-02-01 17:42   ` Torvald Riegel
2012-02-01 19:40     ` Jakub Jelinek
2012-02-01 20:01       ` Linus Torvalds
2012-02-01 20:16         ` Jakub Jelinek
2012-02-01 20:44           ` Linus Torvalds
2012-02-02 15:58             ` Aldy Hernandez
2012-02-02 16:28               ` Michael Matz
2012-02-02 17:51                 ` Linus Torvalds
2012-02-01 20:19         ` Linus Torvalds
2012-02-02  9:46           ` Richard Guenther
2012-02-01 19:44     ` Boehm, Hans
2012-02-01 19:54       ` Jeff Law
2012-02-01 19:47     ` Linus Torvalds
2012-02-01 19:58       ` Alan Cox
2012-02-01 20:41       ` Torvald Riegel
2012-02-01 20:59         ` Linus Torvalds
2012-02-01 21:24           ` Torvald Riegel
2012-02-01 21:55             ` Linus Torvalds
2012-02-01 21:25           ` Boehm, Hans
2012-02-01 22:27             ` Linus Torvalds
2012-02-01 22:45           ` Paul E. McKenney
2012-02-01 23:11             ` Linus Torvalds [this message]
2012-02-02 18:42               ` Paul E. McKenney
2012-02-02 19:08                 ` Linus Torvalds
2012-02-02 19:37                   ` Paul E. McKenney
2012-02-03 16:38                     ` Andrew MacLeod
2012-02-03 17:16                       ` Linus Torvalds
2012-02-03 19:16                         ` Andrew MacLeod
2012-02-03 20:00                           ` Linus Torvalds
2012-02-03 20:19                             ` Paul E. McKenney
2012-02-06 15:38                             ` Torvald Riegel
2012-02-10 19:27                             ` Richard Henderson
2012-02-02 11:19           ` Ingo Molnar
2012-02-01 21:04       ` Boehm, Hans
2012-02-02  9:28         ` Bernd Petrovitsch
2012-02-01 17:08 ` Torvald Riegel
2012-02-01 17:29   ` Linus Torvalds
2012-02-01 20:53     ` Torvald Riegel
2012-02-01 21:20       ` Linus Torvalds
2012-02-01 21:37         ` Torvald Riegel
2012-02-01 22:18           ` Boehm, Hans
2012-02-02 11:11 ` James Courtier-Dutton
2012-02-02 11:24   ` Richard Guenther
2012-02-02 11:13 ` David Sterba
2012-02-02 11:23   ` Richard Guenther
2012-02-03  6:45 ` DJ Delorie
2012-02-03  9:37   ` Richard Guenther
2012-02-03 10:03     ` Matthew Gretton-Dann
2012-02-01 17:52 Dennis Clarke

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