From: Vladislav Bolkhovitin <vst@vlnb.net>
To: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86 bitops.h commentary on instruction reordering
Date: Fri, 06 Aug 2004 18:17:04 +0400 [thread overview]
Message-ID: <411392E0.6080507@vlnb.net> (raw)
In-Reply-To: <20040805200622.GA17324@logos.cnet>
So, is there any way to workaround this problem, i.e. prevent bit
operations reordering on non-x86 architectures? Some kinds of memory
barriers?
Vlad
Marcelo Tosatti wrote:
> Hi,
>
> Back when we were discussing the need for a memory barrier in sync_page(),
> it came to me (thanks Andrea!) that the bit operations can be perfectly
> reordered on architectures other than x86.
>
> I think the commentary on i386 bitops.h is misleading, its worth
> to note that that these operations are not guaranteed not to be
> reordered on different architectures.
>
> clear_bit() already does that:
>
> * clear_bit() is atomic and may not be reordered. However, it does
> * not contain a memory barrier, so if it is used for locking purposes,
> * you should call smp_mb__before_clear_bit() and/or smp_mb__after_clear_bit()
> * in order to ensure changes are visible on other processors.
>
> What you think of the following
next prev parent reply other threads:[~2004-08-06 14:14 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-08-05 20:06 [PATCH] x86 bitops.h commentary on instruction reordering Marcelo Tosatti
2004-08-06 14:17 ` Vladislav Bolkhovitin [this message]
2004-08-06 14:33 ` Marcelo Tosatti
2004-08-06 15:36 ` Vladislav Bolkhovitin
2004-08-06 15:53 ` Marcelo Tosatti
2004-08-06 16:52 ` Vladislav Bolkhovitin
2004-08-06 17:09 ` Marcelo Tosatti
2004-08-06 22:33 ` H. Peter Anvin
2004-08-07 1:01 ` Zwane Mwaikambo
2004-08-07 22:16 ` Alan Cox
2004-08-09 15:14 ` Vladislav Bolkhovitin
2004-08-09 15:50 ` Marcelo Tosatti
2004-08-09 17:35 ` Vladislav Bolkhovitin
[not found] ` <20040809183437.GD6361@logos.cnet>
2004-08-09 20:12 ` Vladislav Bolkhovitin
2004-08-09 21:21 ` Alan Cox
2004-08-10 12:28 ` Vladislav Bolkhovitin
2004-08-09 11:58 ` Maciej W. Rozycki
[not found] <2pY7Y-W1-7@gated-at.bofh.it>
[not found] ` <2qdJL-3sh-27@gated-at.bofh.it>
[not found] ` <2qePx-4eM-21@gated-at.bofh.it>
[not found] ` <2qf8S-4pI-31@gated-at.bofh.it>
[not found] ` <2qg4V-54c-17@gated-at.bofh.it>
[not found] ` <2qgoh-5og-29@gated-at.bofh.it>
[not found] ` <2qhkn-649-41@gated-at.bofh.it>
[not found] ` <2rkgh-zP-45@gated-at.bofh.it>
[not found] ` <2rlFk-1wC-27@gated-at.bofh.it>
[not found] ` <2rmhX-20I-17@gated-at.bofh.it>
[not found] ` <2roWw-40d-19@gated-at.bofh.it>
[not found] ` <2roWw-40d-17@gated-at.bofh.it>
2004-08-09 21:23 ` Andi Kleen
2004-08-10 12:26 ` Vladislav Bolkhovitin
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