On 23/06/2020 22:01, Jens Axboe wrote: > On 6/23/20 5:57 AM, Pavel Begunkov wrote: >> On 23/06/2020 05:18, Jens Axboe wrote: >>> On 6/22/20 8:07 PM, Jens Axboe wrote: >>>> On 6/22/20 4:16 PM, Pavel Begunkov wrote: >>>>> io_do_iopoll() won't do anything with a request unless >>>>> req->iopoll_completed is set. So io_complete_rw_iopoll() has to set >>>>> it, otherwise io_do_iopoll() will poll a file again and again even >>>>> though the request of interest was completed long ago. >>>> >>>> I need to look at this again, because with this change, I previously >>>> got various use-after-free. I haven't seen any issues with it, but >>>> I agree, from a quick look that I'm not quite sure how it's currently >>>> not causing hangs. Yet I haven't seen any, with targeted -EAGAIN >>>> testing. >> >> Can io_complete_rw_iopoll() get -EAGAIN after being successfully enqueued >> (i.e. EIOCBQUEUED)? It's reliably fails for me, because my hacked nullblk >> _can_ (i.e. probabilistically returns BLK_STS_AGAIN from ->iopoll()). > > Yes it can. The primary example would be a polled bio that gets split, into > let's say 4 bio's. First one queues fine, but one of the subsequent ones > run into request allocation failures and it gets marked as -EAGAIN. Right, thanks for the explanation. And that's the case where io_uring fails. Now I tested all kinds of -EAGAIN to be sure. -- Pavel Begunkov
