Matthew Wilcox wrote: > On Tue, Mar 10, 2009 at 10:25:44PM -0500, Mike Christie wrote: >> atomic_set(&hba->state, SOME_STATE_VALUE); >> >> in a interrupt or thread or tasklet then in another thread they will do >> >> if (atomic_read(&hba->state) == SOME_STATE_VALUE)) >> >> Does this mean that the drivers should be doing a >> >> atomic_set(&hba->state, SOME_STATE_VALUE); >> smp_mb(); > > Possibly "smp_mb__after_atomic_inc()" might be correct. Is this guaranteed to work with anything else than atomic_inc? Mike, it's also important to remember that barriers will be needed at the reader place too (/if/ there actually are ordering requirements, that is). E.g. in the writer: atomic_set(&hba->x, new_x); smp_wmb(); hba->y = new_y; And in the reader: y = hba->y; smp_rmb(); x = atomic_read(&hba->x); do_something(x, y); You would do this if you have a requirement that a reader needs 'x' to always be at least as new as 'y', IOW would work incorrectly if an outdated x would be used together with a current y. This only works though if the reader can safely operate on an outdated 'y' + a current 'x'. If neither current x + old y nor old x + current y can be safely combined, then you need to wrap their write and read accesses into lock- or mutex- protected sections. -- Stefan Richter -=====-==--= --== -=-== http://arcgraph.de/sr/ -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
