Re: [PATCH -rt 4/5] use migrate_disable for __local_begin

Peter Zijlstra
2007-07-14T17:32:50Z

On Sat, 2007-07-14 at 13:16 -0400, Mathieu Desnoyers wrote:
> * Peter Zijlstra (a.p.zijlstra@chello.nl) wrote:
> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> > ---
> > include/asm-i386/local.h | 7 ++++---
> > include/asm-x86_64/local.h | 7 ++++---
> > 2 files changed, 8 insertions(+), 6 deletions(-)
> >
> > Index: linux-2.6/include/asm-i386/local.h
> > ===================================================================
> > --- linux-2.6.orig/include/asm-i386/local.h
> > +++ linux-2.6/include/asm-i386/local.h
> > @@ -197,11 +197,12 @@ static __inline__ long local_sub_return(
> > #define __local_begin(__flags) \
> > { \
> > (__flags) = 0; \
> > - preempt_disable(); \
> > + migrate_disable(); \
>
> Brrrr. That's wrong. Your non atomic __local*() updates only makes sense
> when preempt_disable/enable() protects them from concurrent threads on
> the same CPU, which is not the case of migrate_disable/enable(). This is
> why I suggest that you use local_begin/end() mapped to
> migrate_disable/enable() for normal local variables, and, if you really
> want a __local_begin/end(), then it should be mapped to
> preempt_disable/enable() and should state that it provides no protection
> against interrupts.

Sure, but on -rt it does suffice, this part of the patch is rather WIP.