linux-kernel - Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobbered unnecessarily

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Date:	Wed, 25 Jul 2007 07:37:41 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Trond Myklebust <trond.myklebust@....uio.no>,
	Satyam Sharma <ssatyam@....iitk.ac.in>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	David Howells <dhowells@...hat.com>,
	Nick Piggin <nickpiggin@...oo.com.au>, Andi Kleen <ak@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 6/8] i386: bitops: Don't mark memory as clobbered
	unnecessarily

On Tue, 2007-07-24 at 11:13 -0700, Linus Torvalds wrote:
> 
> IOW, if you do a spinlock with the bitops, the locking side should be
> able 
> to use a "test_and_set_bit()" on its own, but the unlocking side
> should be
> 
>         smp_mb__before_clear_bit();
>         clear_bit();
> 
> because the ones that don't return a value also don't imply a memory 
> barrier.

Yup. But I much prefer Nick's clear_bit_unlock() :-)

Ben.


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