On 2/3/22 9:49 AM, Usama Arif wrote: >> One thing that both mine and your version suffers from is if someone >> does an eventfd unregister, and then immediately does an eventfd >> register. If the rcu grace period hasn't passed, we'll get -EBUSY on >> trying to do that, when I think the right behavior there would be to >> wait for the grace period to pass. >> >> I do think we need to handle that gracefully, spurious -EBUSY is >> impossible for an application to deal with. > > I don't think my version would suffer from this as its protected by > locks? The mutex_unlock on ev_fd_lock in unregister happens only after > the call_rcu. And the mutex is locked in io_eventfd_register at the > start, so wouldnt get the -EBUSY if there is a register immediately > after unregister? The call_rcu() just registers it for getting the callback when the grace period has passed, it doesn't mean it's done by the time it returns. Hence there's definitely a window where you can enter io_uring_register() with the callback still being pending, and you'd get -EBUSY from that. -- Jens Axboe
