On Thu, Mar 29, 2018 at 10:33:05PM +0200, Christoph Hellwig wrote: > The upcoming aio poll support would like to be able to complete the > iocb inline from the cancellation context, but that would cause a > double lock of ctx_lock with the current locking scheme. Move the > cancelation outside the context lock to avoid this reversal, which > suits the existing usb gadgets users just fine as well (in fact > both unconditionally disable irqs and thus seem broken without > this change). > > To make this safe aio_complete needs to check if this call should > complete the iocb. If it didn't the callers must not release any > other resources.
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. 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.
