Messages in this thread | | | Date | Thu, 30 Mar 2006 18:37:32 -0800 (PST) | From | Christoph Lameter <> | Subject | RE: Synchronizing Bit operations V2 |
| |
On Thu, 30 Mar 2006, Chen, Kenneth W wrote:
> > > 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?
For Option(1)
smp_mb__before_clear_bit() clear_bit(...)(
For Option(2)
clear_bit() smb_mp_after_clear_bit();
Both have either acquire or release semantics but do not have the effect of a barrier as required by the macros.
Note that both before and after are used in the core kernel code. Both must work correctly.
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |