On 9/2/20 10:00 AM, Pavel Begunkov wrote: > 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? Yeah, the posted version did get it right: https://lore.kernel.org/io-uring/5d91a8ea-5748-803a-d2dc-ef21fe27e39e@xxxxxxxxx/T/#u -- Jens Axboe
