From: Kevin Wolf <kwolf@redhat.com>
To: Fabian Ebner <f.ebner@proxmox.com>
Cc: "open list:Linux io_uring" <qemu-block@nongnu.org>,
Stefan Hajnoczi <stefanha@gmail.com>,
Julia Suvorova <jusual@redhat.com>,
qemu-devel@nongnu.org, Max Reitz <mreitz@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>,
Aarushi Mehta <mehta.aaru20@gmail.com>,
Stefano Garzarella <sgarzare@redhat.com>
Subject: Re: [PATCH v2] block/io_uring: resubmit when result is -EAGAIN
Date: Mon, 2 Aug 2021 14:40:36 +0200 [thread overview]
Message-ID: <YQfnxLROKL/JUKyF@redhat.com> (raw)
In-Reply-To: <20210729091029.65369-1-f.ebner@proxmox.com>
Am 29.07.2021 um 11:10 hat Fabian Ebner geschrieben:
> 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;
> }
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Question about the preexisting code, though: luring_resubmit() requires
that the caller calls ioq_submit() later so that the request doesn't
just sit in a queue without getting any attention, but actually gets
submitted to the kernel.
In the call chain ioq_submit() -> luring_process_completions() ->
luring_resubmit(), who takes care of that?
Kevin
next prev parent reply other threads:[~2021-08-02 12:42 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-29 9:10 [PATCH v2] block/io_uring: resubmit when result is -EAGAIN Fabian Ebner
2021-07-29 9:54 ` Stefano Garzarella
2021-07-29 16:15 ` Stefan Hajnoczi
2021-08-02 12:40 ` Kevin Wolf [this message]
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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