Re: [PATCH] Keys: Improve usage of memory barriers and remove IRQ disablement

["David S. Miller" <davem@davemloft.net>]

From: Nick Piggin <nickpiggin@yahoo.com.au>
Date: Wed, 05 Apr 2006 19:23:58 +1000

> David Howells wrote:
> > Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> 
> > | 	int atomic_inc_and_test(atomic_t *v);
> > | 	int atomic_dec_and_test(atomic_t *v);
> > | 
> > | These two routines increment and decrement by 1, respectively, the
> > | given atomic counter.  They return a boolean indicating whether the
> > | resulting counter value was zero or not.
> > | 
> > | It requires explicit memory barrier semantics around the operation as
> > | above.
> > 
> > Note the last paragraph.  "It requires" should be "They require", but the
> > sense would seem to be obvious.  However, it's not clear on a second reading
> > as to whether this is an instruction to the _caller_ or an instruction to the
> > arch _implementer_.
> > 
> 
> Yes, I remember Dave M clarified this sometime ago (on lkml I guess). It
> is a little confusing, but I think the wording is for the implementer's
> point of view. Dave will pull me up if I'm wrong...

Any routine which returns state must have the barriers in the arch
implementation.  These two routines returns state.