Re: [PATCH] move xchg/cmpxchg to atomic.h

[Andi Kleen]

On Tue, Jan 02, 2001 at 11:22:42AM +0000, Matthew Wilcox wrote:
> On Tue, Jan 02, 2001 at 01:03:48AM -0800, David S. Miller wrote:
> > If you require an external agent (f.e. your spinlock) because you
> > cannot implement xchg with a real atomic sequence, this breaks the
> > above assumptions.
> 
> We really can't.  We _only_ have load-and-zero.  And it has to be 16-byte
> aligned.  xchg() is just not something the CPU implements.

The network code relies on the reader-xchg semantics David described in 
several places.

-Andi