linux-kernel - Re: [PATCH] WorkStruct: Implement generic UP cmpxchg() where an arch doesn't support it

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Message-ID: <Pine.LNX.4.64.0612061152290.3542@woody.osdl.org>
Date:	Wed, 6 Dec 2006 11:54:04 -0800 (PST)
From:	Linus Torvalds <torvalds@...l.org>
To:	Matthew Wilcox <matthew@....cx>
cc:	Al Viro <viro@....linux.org.uk>,
	Christoph Lameter <clameter@....com>,
	Russell King <rmk+lkml@....linux.org.uk>,
	David Howells <dhowells@...hat.com>,
	Andrew Morton <akpm@...l.org>,
	linux-arm-kernel@...ts.arm.linux.org.uk,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH] WorkStruct: Implement generic UP cmpxchg() where an arch
 doesn't support it



On Wed, 6 Dec 2006, Matthew Wilcox wrote:
> 
> That doesn't help, since assignment can't be guarded by any lock.

True. Pure assignment will be lost, and is only ok for the case of a pure 
initializer (where nobody can see the old state).

Your problem will be, of course, that any architecture that does this in 
hardware will just DoTheRightThing, and as such, broken architectures with 
bad locking primitives will have to test and do source-level analysis 
more.

		Linus
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