From: Fabian Ebner <f.ebner@proxmox.com>
To: qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>,
"open list:Linux io_uring" <qemu-block@nongnu.org>,
Stefan Hajnoczi <stefanha@gmail.com>,
Julia Suvorova <jusual@redhat.com>, Max Reitz <mreitz@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>,
Fabian Ebner <f.ebner@proxmox.com>,
Aarushi Mehta <mehta.aaru20@gmail.com>,
Stefano Garzarella <sgarzare@redhat.com>
Subject: [PATCH v2] block/io_uring: resubmit when result is -EAGAIN
Date: Thu, 29 Jul 2021 11:10:29 +0200 [thread overview]
Message-ID: <20210729091029.65369-1-f.ebner@proxmox.com> (raw)
Linux SCSI can throw spurious -EAGAIN in some corner cases in its
completion path, which will end up being the result in the completed
io_uring request.
Resubmitting such requests should allow block jobs to complete, even
if such spurious errors are encountered.
Co-authored-by: Stefan Hajnoczi <stefanha@gmail.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>
---
Changes from v1:
* Focus on what's relevant for the patch itself in the commit
message.
* Add Stefan's comment.
* Add Stefano's R-b tag (I hope that's fine, since there was no
change code-wise).
block/io_uring.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/block/io_uring.c b/block/io_uring.c
index 00a3ee9fb8..dfa475cc87 100644
--- a/block/io_uring.c
+++ b/block/io_uring.c
@@ -165,7 +165,21 @@ static void luring_process_completions(LuringState *s)
total_bytes = ret + luringcb->total_read;
if (ret < 0) {
- if (ret == -EINTR) {
+ /*
+ * Only writev/readv/fsync requests on regular files or host block
+ * devices are submitted. Therefore -EAGAIN is not expected but it's
+ * known to happen sometimes with Linux SCSI. Submit again and hope
+ * the request completes successfully.
+ *
+ * For more information, see:
+ * https://lore.kernel.org/io-uring/20210727165811.284510-3-axboe@kernel.dk/T/#u
+ *
+ * If the code is changed to submit other types of requests in the
+ * future, then this workaround may need to be extended to deal with
+ * genuine -EAGAIN results that should not be resubmitted
+ * immediately.
+ */
+ if (ret == -EINTR || ret == -EAGAIN) {
luring_resubmit(s, luringcb);
continue;
}
--
2.30.2
next reply other threads:[~2021-07-29 9:13 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-29 9:10 Fabian Ebner [this message]
2021-07-29 9:54 ` [PATCH v2] block/io_uring: resubmit when result is -EAGAIN Stefano Garzarella
2021-07-29 16:15 ` Stefan Hajnoczi
2021-08-02 12:40 ` Kevin Wolf
2021-08-04 14:50 ` Stefano Garzarella
2021-08-04 16:52 ` Kevin Wolf
2021-08-05 8:31 ` Stefano Garzarella
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