linux-kernel - Re: [PATCH 0/2] uring

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Message-ID: <CADUfDZqa5v7Rb-EXp-v_iMXAESts8u-DisMtjdBEu2+kK-ykeQ@mail.gmail.com>
Date: Wed, 12 Feb 2025 15:46:34 -0800
From: Caleb Sander Mateos <csander@...estorage.com>
To: Keith Busch <kbusch@...nel.org>
Cc: Jens Axboe <axboe@...nel.dk>, Pavel Begunkov <asml.silence@...il.com>, 
	Riley Thomasson <riley@...estorage.com>, io-uring@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] uring_cmd SQE corruptions

On Wed, Feb 12, 2025 at 3:21 PM Keith Busch <kbusch@...nel.org> wrote:
>
> On Wed, Feb 12, 2025 at 03:07:30PM -0800, Caleb Sander Mateos wrote:
> >
> > Yes, we completely agree. We are working on incorporating Keith's
> > patchset now. It looks like there is still an open question about
> > whether userspace will need to enforce ordering between the requests
> > (either using linked operations or waiting for completions before
> > submitting the subsequent operations).
>
> In its current form, my series depends on you *not* using linked
> requests. I didn't think it would be a problem as it follows an existing
> pattern from the IORING_OP_FILES_UPDATE operation. That has to complete
> in its entirety before prepping any subsequent commands that reference
> the index, and using links would get the wrong results.

As implementers of a ublk server, we would also prefer the current
interface in your patch series! Having to explicitly order the
requests would definitely make the interface more cumbersome and
probably less performant. I was just saying that Ming and Pavel had
raised some concerns about guaranteeing the order in which io_uring
issues SQEs. IORING_OP_FILES_UPDATE is a good analogy. Do we have any
examples of how applications use it? Are they waiting for a
completion, linking it, or relying on io_uring to issue it
synchronously?