RE: Synchronizing Bit operations V2

["Chen, Kenneth W" <kenneth.w.chen@intel.com>]

Christoph Lameter wrote on Thursday, March 30, 2006 5:38 PM
> > Christoph Lameter wrote on Thursday, March 30, 2006 5:13 PM
> > > Then there will no barrier since clear_bit only has acquire semantics.
> > > This is a  bug in bit operations since smb_mb__before_clear_bit does
> > > not work as documentted.
> > 
> > Well, please make up your mind with:
> > 
> > Option (1):
> > 
> > #define clear_bit                     clear_bit_mode(..., RELEASE)
> > #define Smp_mb__before_clear_bit      do { } while (0)
> > #define Smp_mb__after_clear_bit       smp_mb()
> > 
> > Or option (2):
> > 
> > #define clear_bit                     clear_bit_mode(..., ACQUIRE)
> > #define Smp_mb__before_clear_bit      smp_mb()
> > #define Smp_mb__after_clear_bit       do { } while (0)
> > 
> > I'm fine with either one.
> 
> Neither one is correct because there will always be one combination of 
> clear_bit with these macros that does not generate the required memory 
> barrier.

Can you give an example?  Which combination?

- Ken