From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
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 19:58:19 +0000 [thread overview]
Message-ID: <20120201195819.76357d79@pyramind.ukuu.org.uk> (raw)
In-Reply-To: <CA+55aFw=z2SKFGoSE5e_0ZmKcAAjK5q0DBM4PaxBH2D9tuikzA@mail.gmail.com>
> So here's basically what the kernel needs:
>
> - if we don't touch a field, the compiler doesn't touch it.
>
> This is the rule that gcc now violates with bitfields.
>
> This is a gcc bug. End of story. The "volatile" example proves it -
> anybody who argues otherwise is simply wrong, and is just trying to
> make excuses.
C historically didn't make this guarantee because a lot of processors
couldn't make it because they didn't have things like byte accessors (In
fact I suspect early ARM cannot make it for example).
Not meeting it for types where you can do is a bit rude however and
really ought to be an option (speed v sanity).
> See above: it's not the "state" that is accessed concurrently. It's
> the code. If you ever try to mark state, you've already lost. The same
> "state" can be atomic or not depending on context. It's not about the
> state or the data structures, and it never will be.
There are optimisation cases - where you can prove access properties are
safe (eg local variables some times) but they should be exactly that -
optimisations.
Alan
next prev parent reply other threads:[~2012-02-01 19:57 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 [this message]
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
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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