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From: David Howells <dhowells@redhat.com>
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Subject: Re: [PATCH] WorkStruct: Implement generic UP cmpxchg() where an arch doesn't support it 
Date: Wed, 06 Dec 2006 19:43:15 +0000
Message-ID: <28576.1165434195@redhat.com>
Sender: linux-arch-owner@vger.kernel.org
To: Matthew Wilcox <matthew@wil.cx>
Cc: Linus Torvalds <torvalds@osdl.org>, Al Viro <viro@ftp.linux.org.uk>, Christoph Lameter <clameter@sgi.com>, Russell King <rmk+lkml@arm.linux.org.uk>, David Howells <dhowells@redhat.com>, Andrew Morton <akpm@osdl.org>, linux-arm-kernel@lists.arm.linux.org.uk, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-arch@vger.kernel.org
List-ID: <linux-arch.vger.kernel.org>

Matthew Wilcox <matthew@wil.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