On Thu, Mar 29, 2018 at 11:35:00PM +0100, Al Viro wrote: > Uh-oh... What happens to existing users of kiocb_set_cancel_fn() now? > AFAICS, those guys will *not* get aio_kiocb freed at all in case of > io_cancel(2). Look: we mark them with AIO_IOCB_CANCELLED and > call whatever ->ki_cancel() the driver has set. Later the damn > thing calls ->ki_complete() (i.e. aio_complete_rw()), which calls > aio_complete(iocb, res, res2, 0) and gets false. Nothing's freed, > struct file is leaked. True, we'd need a complete call from it. > Frankly, the more I look at that, the less I like what you've done > with ->ki_cancel() overloading. In regular case it's just accelerating > the call of ->ki_complete(), which will do freeing. Here you have > ->ki_cancel() free the damn thing, with the resulting need to play > silly buggers with locking, freeing logics in aio_complete(), etc. I don't really like it all that much either, but I also think the current model is pretty broken - called under spinlock with irqs disabled is not even what the current users expect. Second issue with the existing ki_cancel is that kiocb_set_cancel_fn operates on a kiocb, but expects that to be embedded in an aio_kiocb, which might not always be the case, althought in-kernel I/O is unlikely to be used on them. And based on all of these I bet gadget aio cancel is basically untested. Anyway, I guess splitting poll direct cancel out in a way that doesn't overload ->ki_cancel might be a good idea. It all is inside aio.c so simply switching on the opcode similar to the submission path might be one option, or having separate methods. Moving ki_cancel to kiocb would also solve above mismatch issue.
