Lai, I didn't read this discussion except the code posted by Michel. I'll try to read this patch carefully later, but I'd like to ask a couple of questions. This version looks more complex than Michel's, why? Just curious, I am trying to understand what I missed. See http://marc.info/?l=linux-kernel&m=136196350213593 And I can't understand FALLBACK_BASE... OK, suppose that CPU_0 does _write_unlock() and releases ->fallback_rwlock. CPU_1 does _read_lock(), and ... > +void lg_rwlock_local_read_lock(struct lgrwlock *lgrw) > +{ > + struct lglock *lg = &lgrw->lglock; > + > + preempt_disable(); > + rwlock_acquire_read(&lg->lock_dep_map, 0, 0, _RET_IP_); > + if (likely(!__this_cpu_read(*lgrw->reader_refcnt))) { > + if (!arch_spin_trylock(this_cpu_ptr(lg->lock))) { _trylock() fails, > + read_lock(&lgrw->fallback_rwlock); > + __this_cpu_add(*lgrw->reader_refcnt, FALLBACK_BASE); so we take ->fallback_rwlock and ->reader_refcnt == FALLBACK_BASE. CPU_0 does lg_global_unlock(lgrw->lglock) and finishes _write_unlock(). Interrupt handler on CPU_1 does _read_lock() notices ->reader_refcnt != 0 and simply does this_cpu_inc(), so reader_refcnt == FALLBACK_BASE + 1. Then irq does _read_unlock(), and > +void lg_rwlock_local_read_unlock(struct lgrwlock *lgrw) > +{ > + switch (__this_cpu_dec_return(*lgrw->reader_refcnt)) { > + case 0: > + lg_local_unlock(&lgrw->lglock); > + return; > + case FALLBACK_BASE: > + __this_cpu_sub(*lgrw->reader_refcnt, FALLBACK_BASE); > + read_unlock(&lgrw->fallback_rwlock); hits this case? Doesn't look right, but most probably I missed something. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
