On Mon, 20 May 2002, David S. Miller wrote: > Such rule does not even make this piece of code legal. Consider: > > task1:cpu0: x = counters[smp_processor_id()]; > cpu0: PREEMPT > task2:cpu0: x = counters[smp_processor_id()]; > task2:cpu0: counters[smp_processor_id()] = x + 1; > cpu0: PREEMPT > task1:cpu0: counters[smp_processor_id()] = x + 1; > full garbage > > But it does bring up important point, preemption people need to > fully audit entire networking. > > It is totally broken by preemption the more I think about it. > > At the very beginning, all the SNMP counter bumping tricks will > totally fail with preemption enabled. > A lot of the synchronization between process context and interrupt context is based on per-cpu data structures or simple locks (without disabling irq's globally) eg: softnet_data queue (we only disable local interrupts), and synchronization between tcp_readmsg() and tcp_rcv() over the receive queue would get confused (lock.users flag would be different on another CPU).. Wonder how any of it could possibly work.. thanks, Nivedita - : send the line "unsubscribe linux-net" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
