From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Jamie Lokier <jamie@shareable.org>,
Catalin Marinas <catalin.marinas@arm.com>,
linux-arm-kernel@lists.arm.linux.org.uk,
linux-kernel@vger.kernel.org,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: Broken ARM atomic ops wrt memory barriers (was : [PATCH] Add cmpxchg support for ARMv6+ systems)
Date: Wed, 27 May 2009 09:56:31 +0100 [thread overview]
Message-ID: <20090527085631.GA18768@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <20090527012243.GB29692@Krystal>
On Tue, May 26, 2009 at 09:22:43PM -0400, Mathieu Desnoyers wrote:
> My point was not about the wmb() : we _clearly_ need a dmb there. My
> point is about the hidden
>
> smp_read_barrier_depends() in rcu_dereference() :
>
> cpyptr = ptr;
> smp_read_barrier_depends();
> access *cpyptr data
>
> Which is needed to make sure we update our global view of memory between
> the pointer value read and the moment we read the data pointed to. This
> makes sure the data read is not garbage.
There is a dependency between reading 'ptr' and reading 'data'.
I think there was a paragraph in the ARM ARM about this which says
that they happen in program order, but I don't have access at the
moment to the ARM ARM to check right now.
next prev parent reply other threads:[~2009-05-27 8:57 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20090422171703.19555.83629.stgit@pc1117.cambridge.arm.com>
[not found] ` <20090423141248.22193.10543.stgit@pc1117.cambridge.arm.com>
[not found] ` <20090524131636.GB3159@n2100.arm.linux.org.uk>
2009-05-24 14:56 ` Mathieu Desnoyers
2009-05-25 13:20 ` Jamie Lokier
2009-05-25 15:17 ` Mathieu Desnoyers
2009-05-25 16:19 ` Russell King - ARM Linux
2009-05-25 17:29 ` Mathieu Desnoyers
2009-05-25 19:34 ` Russell King - ARM Linux
2009-05-25 20:05 ` Mathieu Desnoyers
2009-05-26 11:29 ` Catalin Marinas
2009-05-25 19:56 ` Russell King - ARM Linux
2009-05-25 20:22 ` Mathieu Desnoyers
2009-05-25 21:45 ` Broken ARM (and powerpc ?) futex wrt memory barriers Mathieu Desnoyers
2009-05-25 21:57 ` Russell King - ARM Linux
2009-05-25 22:27 ` Mathieu Desnoyers
2009-05-26 14:59 ` Broken ARM atomic ops wrt memory barriers (was : [PATCH] Add cmpxchg support for ARMv6+ systems) Russell King - ARM Linux
2009-05-26 15:36 ` Mathieu Desnoyers
2009-05-26 15:59 ` Russell King - ARM Linux
2009-05-26 17:23 ` Mathieu Desnoyers
2009-05-26 18:23 ` Russell King - ARM Linux
2009-05-26 19:17 ` Jamie Lokier
2009-05-26 19:56 ` Russell King - ARM Linux
2009-05-27 1:22 ` Mathieu Desnoyers
2009-05-27 8:56 ` Russell King - ARM Linux [this message]
2009-05-27 9:18 ` Catalin Marinas
2009-05-27 9:14 ` Catalin Marinas
2009-05-27 14:52 ` Mathieu Desnoyers
2009-05-27 15:59 ` Paul E. McKenney
2009-05-27 16:02 ` Mathieu Desnoyers
2009-05-27 20:55 ` Paul E. McKenney
2009-05-27 18:40 ` Mathieu Desnoyers
2009-05-28 18:20 ` Russell King - ARM Linux
2009-05-28 18:38 ` Mathieu Desnoyers
2009-05-28 18:40 ` Russell King - ARM Linux
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