Re: [Linux-ia64] spin_unlock() problem

[David Mosberger <davidm@napali.hpl.hp.com>]

>>>>> On 07 Apr 2003 19:13:40 -0400, Jes Sorensen <jes@wildopensource.com> said:

  Jes> This is the situation I was trying to fix, adding a wmb() to
  Jes> spin_unlock() seems the only way to get around it as far as I can see.
  Jes> I take it you agree then?

As Jim pointed out, there is an anologous problem on the read-side.
Declaring the pointer "volatile" fixes the problem for ia64 and is
arguably the right (logical) thing to do anyhow.

However, it won't fix the problem for Alpha though: there you'd need
to add rmb() between the two reads on cpu2() (read_barrier_depends()
only guarantees ordering for data-dependent reads, so it won't work
here).

So, the most portable way to fix this is to add a wmb() on the side of
cpu1() and rmb() on the read side.

	--david