Messages in this thread | | | Date | Thu, 13 Nov 2003 12:10:42 +0100 | From | Jens Axboe <> | Subject | Re: AS spin lock bugs |
| |
On Thu, Nov 13 2003, Jens Axboe wrote: > On Thu, Nov 13 2003, Nick Piggin wrote: > > > > > > Jens Axboe wrote: > > > > >On Thu, Nov 13 2003, Jens Axboe wrote: > > > > > >>@@ -959,12 +960,12 @@ > > >> if (!aic) > > >> return; > > >> > > >>- spin_lock(&aic->lock); > > >>+ spin_lock_irqsave(&aic->lock, flags); > > >> if (arq->is_sync == REQ_SYNC) { > > >> set_bit(AS_TASK_IORUNNING, &aic->state); > > >> aic->last_end_request = jiffies; > > >> } > > >>- spin_unlock(&aic->lock); > > >>+ spin_unlock_irqrestore(&aic->lock, flags); > > >> > > >> put_io_context(arq->io_context); > > >>} > > >> > > > > > >BTW, this looks bogus. Why do you need any locking there? > > > > > > > To prevent a request completion on another queue on another CPU from > > racing with request insertion: last_end_request is undefined if the > > flag is not set. I guess you could flip the statements and put a > > smp_mb between them. Probably not worth the trouble though. > > No better to make it explicit, probably doesn't matter much in > real-life. Thanks for the clarifications.
Ah, it would be clearer as:
if (arq->is_sync == REQ_SYNC) { spin_lock(&aic->lock); set_bit(AS_TASK_IORUNNING, &aic->state); aic->last_end_request = jiffies; spin_unlock(&aic->lock); }
Then it doesn't need comments :)
-- Jens Axboe
- 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/
| |