On Tue, Oct 24, 2017 at 11:34:13AM +0200, Ingo Molnar wrote:
>
> * Johannes Berg <johannes@xxxxxxxxxxxxxxxx> wrote:
>
> > On Mon, 2017-10-23 at 21:07 +0000, Paul E. McKenney wrote:
> > > From: Mark Rutland <mark.rutland@xxxxxxx>
> > >
> > > For several reasons, it is desirable to use {READ,WRITE}_ONCE() in
> > > preference to ACCESS_ONCE(), and new code is expected to use one of the
> > > former. So far, there's been no reason to change most existing uses of
> > > ACCESS_ONCE(), as these aren't currently harmful.
> > >
> > > However, for some features it is necessary to instrument reads and
> > > writes separately, which is not possible with ACCESS_ONCE(). This
> > > distinction is critical to correct operation.
> > >
> > > It's possible to transform the bulk of kernel code using the Coccinelle
> > > script below. However, this doesn't pick up some uses, including those
> > > in <linux/average.h>. As a preparatory step, this patch converts the
> > > file to use {READ,WRITE}_ONCE() consistently.
> > >
> > > At the same time, this patch addds missing includes necessary for
> > > {READ,WRITE}_ONCE(), *BUG_ON*(), and ilog2().
> > >
> > > ----
> > > virtual patch
> > >
> > > @ depends on patch @
> > > expression E1, E2;
> > > @@
> > >
> > > - ACCESS_ONCE(E1) = E2
> > > + WRITE_ONCE(E1, E2)
> > >
> > > @ depends on patch @
> > > expression E;
> > > @@
> > >
> > > - ACCESS_ONCE(E)
> > > + READ_ONCE(E)
> > > ----
> > >
> > > Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
> > > Cc: Johannes Berg <johannes.berg@xxxxxxxxx>
> >
> > Reviewed-by: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
>
> Thanks!
>
> > Let me know if you want me to apply this, since I seem to be the
> > average.h maintainer :-)
>
> Would be nice to keep these patches together if possible, so that we can remove
> ACCESS_ONCE() - or at least add a build warning.
My goal is to remove it. After all, I am the guy who added it. ;-)
Thanx, Paul
