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

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Message-ID: <28576.1165434195@redhat.com>
Date:	Wed, 06 Dec 2006 19:43:15 +0000
From:	David Howells <dhowells@...hat.com>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Linus Torvalds <torvalds@...l.org>,
	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 

Matthew Wilcox <matthew@....cx> wrote:

> > Ok. For SMP-safety, it's important that any architecture that can't do 
> > this needs to _share_ the same spinlock (on SMP only, of course) that it 
> > uses for the bitops. 
> 
> That doesn't help, since assignment can't be guarded by any lock.

It's not a problem for workqueues, since the only direct assignment to the
management member variable is during initialisation.

But in general cmpxchg() might be a problem with respect to assignment.

atomic_cmpxchg() should be safe wrt atomic_set().

David
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