On 02/09/2020 18:35, Jens Axboe wrote: > On 9/2/20 9:26 AM, Pavel Begunkov wrote: >> On 02/09/2020 17:45, Jens Axboe wrote: >>> On 9/2/20 4:09 AM, Norman Maurer wrote: >>>> Hi there, >>>> >>>> We are currently working on integrating io_uring into netty and found >>>> some “suprising” behaviour which seems like a bug to me. >>>> >>>> When a socket is marked as non blocking (accepted with O_NONBLOCK flag >>>> set) and there is no data to be read IORING_OP_READ should complete >>>> directly with EAGAIN or EWOULDBLOCK. This is not the case and it >>>> basically blocks forever until there is some data to read. Is this >>>> expected ? >>>> >>>> This seems to be somehow related to a bug that was fixed for >>>> IO_URING_ACCEPT with non blocking sockets: >>>> >>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v5.8&id=e697deed834de15d2322d0619d51893022c90ea2 >>> >>> I agree with you that this is a bug, in general it's useful (and >>> expected) that we'd return -EAGAIN for that case. I'll take a look. >>> >> >> That's I mentioned that doing retries for nonblock requests in >> io_wq_submit_work() doesn't look consistent. I think killing it >> off may help. > > Right, we should not retry those _in general_, the exception is regular > files or block devices to handle IOPOLL retry where we do need it. The > below is what I came up with for this one. Might not hurt to make this > more explicit for 5.10. Hmm, I didn't checked it, but if we > > > commit c78e0f02c3861b5b176b2f79552677b3604deb76 > Author: Jens Axboe <axboe@xxxxxxxxx> > Date: Wed Sep 2 09:30:31 2020 -0600 > > io_uring: no read-retry on -EAGAIN error and O_NONBLOCK marked file > > Actually two things that need fixing up here: > > - The io_rw_reissue() -EAGAIN retry is explicit to block devices and > regular files, so don't ever attempt to do that on other types of > files. > > - If we hit -EAGAIN on a nonblock marked file, don't arm poll handler for > it. It should just complete with -EAGAIN. > > Cc: stable@xxxxxxxxxxxxxxx > Reported-by: Norman Maurer <norman.maurer@xxxxxxxxxxxxxx> > Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> > > diff --git a/fs/io_uring.c b/fs/io_uring.c > index b1ccd7072d93..dc27cd5b8ad6 100644 > --- a/fs/io_uring.c > +++ b/fs/io_uring.c > @@ -2300,8 +2300,11 @@ static bool io_resubmit_prep(struct io_kiocb *req, int error) > static bool io_rw_reissue(struct io_kiocb *req, long res) > { > #ifdef CONFIG_BLOCK > + umode_t mode = file_inode(req->file)->i_mode; > int ret; > > + if (!S_ISBLK(mode) && !S_ISREG(mode)) > + return false; > if ((res != -EAGAIN && res != -EOPNOTSUPP) || io_wq_current_is_worker()) > return false; > > @@ -3146,6 +3149,9 @@ static int io_read(struct io_kiocb *req, bool force_nonblock, > /* IOPOLL retry should happen for io-wq threads */ > if (!force_nonblock && !(req->ctx->flags & IORING_SETUP_IOPOLL)) > goto done; > + /* no retry on NONBLOCK marked file */ > + if (kiocb->ki_flags & IOCB_NOWAIT) > + goto done; We clearing and setting IOCB_NOWAIT depending on @force_nonblock, so it may not work. E.g. with IOSQE_IO_ASYNC io_read() will clear it at the beginning. Maybe REQ_F_NOWAIT? > /* some cases will consume bytes even on error returns */ > iov_iter_revert(iter, iov_count - iov_iter_count(iter)); > ret = io_setup_async_rw(req, iovec, inline_vecs, iter, false); > -- Pavel Begunkov
