On Thu, Aug 02, 2018 at 06:16:48PM +0200, Christoph Hellwig wrote: > On Thu, Aug 02, 2018 at 05:08:38PM +0100, Al Viro wrote: > > On Thu, Aug 02, 2018 at 06:08:16PM +0200, Christoph Hellwig wrote: > > > On Thu, Aug 02, 2018 at 05:00:32PM +0100, Al Viro wrote: > > > > BTW, what happens if we insert into one queue and immediately get > > > > woken up, even before the damn thing gets to the end of ->poll(), > > > > which proceeds to call poll_wait() again (on another queue)? > > > > AFAICS, apt.error will be set by the second callback and completely > > > > ignored. And so will the return value of ->poll()... > > > > > > > > Sigh... Analysis of that thing is bloody painful, mostly because > > > > it's hard to describe the state... > > > > > > That's the problem with the ->poll interface. We call it, then > > > have magic happen underneath where it might or might not get added > > > to one (or more if we didn't exclude that) waitqueues, and might > > > have actually been worken before return. I can't really think of > > > a good way to do that entirely sanely. > > > > > > Best I can think of is to only allow using file ops that do keyed > > > wakeups and rely on the keyed wakeups alone. I've started coming > > > up with a version of that, but it won't be until tomorrow at least > > > that I can post it. > > > > What does it buy you? You still have to deal with trylock failures > > in wakeup... > > But we'll never re-add an iocb once it has been removed from the > waitqueue. Umm... Frankly, I wonder if the right approach is to declare that if wakeup has happened at all, submit gives up any responsibility. IOW, have aio_poll * create iocb, feed to ->poll() * check if ->head is NULL; if it is, the mask we've got is *all* we are going to get; complete and bugger off. * lock ioctx * insert the sucker into ->active_reqs * lock the queue * check if wakeup has already happened. * if it has - go away, it's submitted * check apt.error; if set, fail with -EINVAL. * check the mask; if nothing of interest is in there, go away * dequeue, unlist, complete and bugger off On cancel side * lock queue * mark it cancelled * removed from queue if it was there * unlock queue On wakeup * mark it woken * complete or schedule completion, which would be where we check if it's marked cancelled - both before vfs_poll() (to avoid calling it if already set) and after (treating cancel during vfs_poll() as "complete and bugger off"). Comments?
