debian/patches/extra/0002-block-io_uring-resubmit-when-result-is-EAGAIN.patch

   1 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
   2 From: Fabian Ebner <f.ebner@proxmox.com>
   3 Date: Fri, 23 Jul 2021 12:42:23 +0200
   4 Subject: [PATCH] block/io_uring: resubmit when result is -EAGAIN
   5
   6 Linux SCSI can throw spurious -EAGAIN in some corner cases in its
   7 completion path, which will end up being the result in the completed
   8 io_uring request.
   9
  10 Resubmitting such requests should allow block jobs to complete, even
  11 if such spurious errors are encountered.
  12
  13 Co-authored-by: Stefan Hajnoczi <stefanha@gmail.com>
  14 Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
  15 Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>
  16 ---
  17  block/io_uring.c | 16 +++++++++++++++-
  18  1 file changed, 15 insertions(+), 1 deletion(-)
  19
  20 diff --git a/block/io_uring.c b/block/io_uring.c
  21 index 00a3ee9fb8..dfa475cc87 100644
  22 --- a/block/io_uring.c
  23 +++ b/block/io_uring.c
  24 @@ -165,7 +165,21 @@ static void luring_process_completions(LuringState *s)
  25          total_bytes = ret + luringcb->total_read;
  26
  27          if (ret < 0) {
  28 -            if (ret == -EINTR) {
  29 +            /*
  30 +             * Only writev/readv/fsync requests on regular files or host block
  31 +             * devices are submitted. Therefore -EAGAIN is not expected but it's
  32 +             * known to happen sometimes with Linux SCSI. Submit again and hope
  33 +             * the request completes successfully.
  34 +             *
  35 +             * For more information, see:
  36 +             * https://lore.kernel.org/io-uring/20210727165811.284510-3-axboe@kernel.dk/T/#u
  37 +             *
  38 +             * If the code is changed to submit other types of requests in the
  39 +             * future, then this workaround may need to be extended to deal with
  40 +             * genuine -EAGAIN results that should not be resubmitted
  41 +             * immediately.
  42 +             */
  43 +            if (ret == -EINTR || ret == -EAGAIN) {
  44                  luring_resubmit(s, luringcb);
  45                  continue;
  46              }
  47 --
  48 2.30.2
  49