Am 18.09.2012 16:24, schrieb Paolo Bonzini: > Il 18/09/2012 13:40, Kevin Wolf ha scritto: >> + qemu_co_mutex_unlock(&s->lock); >> + qemu_co_rwlock_rdlock(&s->l2meta_flush); > > Should this lock be taken in process_l2meta? It's a bit easier to follow.
I'm pretty sure there was a reason, but it isn't obvious any more. I guess I should have put a comment there... Maybe it doesn't exist any more, or maybe it's not that obvious. The difference would be that while waiting for the lock, the original write request could complete instead of waiting as well, and that the lock is potentially taken only in a BH instead of immediately. What happens if bdrv_aio_flush() and bdrv_aio_writev() are both in flight? If the flush runs its stop_l2meta() after the write request has signalled completion, but before the COW coroutine has started, it gets the lock even though a COW must still be processed. I believe we could then return a successful flush when the metadata isn't really on disk yet. So if you agree, I think we need to leave it where it is. Kevin
