Re: [RFC 01/13] io_uring: add infra for uring_cmd completion in submitter-task

From: Luis Chamberlain <mcgrof@kernel.org>
To: Jens Axboe <axboe@kernel.dk>
Cc: "Kanchan Joshi" <joshiiitr@gmail.com>,
	"Kanchan Joshi" <joshi.k@samsung.com>,
	io-uring@vger.kernel.org, linux-nvme@lists.infradead.org,
	linux-block@vger.kernel.org, "Christoph Hellwig" <hch@lst.de>,
	"Keith Busch" <kbusch@kernel.org>,
	"Javier González" <javier@javigon.com>,
	"Anuj Gupta" <anuj20.g@samsung.com>,
	"Pankaj Raghav" <pankydev8@gmail.com>
Subject: Re: [RFC 01/13] io_uring: add infra for uring_cmd completion in submitter-task
Date: Thu, 17 Feb 2022 10:46:36 -0800	[thread overview]
Message-ID: <Yg6YDJHcSh1WPh2+@bombadil.infradead.org> (raw)
In-Reply-To: <b11ede2b-b737-f99a-7b31-20d6b4eccb42@kernel.dk>

On Thu, Feb 17, 2022 at 08:50:59AM -0700, Jens Axboe wrote:
> On 2/17/22 8:39 AM, Kanchan Joshi wrote:
> > On Thu, Feb 17, 2022 at 7:43 AM Luis Chamberlain <mcgrof@kernel.org> wrote:
> >>
> >> On Mon, Dec 20, 2021 at 07:47:22PM +0530, Kanchan Joshi wrote:
> >>> Completion of a uring_cmd ioctl may involve referencing certain
> >>> ioctl-specific fields, requiring original submitter context.
> >>> Export an API that driver can use for this purpose.
> >>> The API facilitates reusing task-work infra of io_uring, while driver
> >>> gets to implement cmd-specific handling in a callback.
> >>>
> >>> Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
> >>> Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
> >>> ---
> >>>  fs/io_uring.c            | 16 ++++++++++++++++
> >>>  include/linux/io_uring.h |  8 ++++++++
> >>>  2 files changed, 24 insertions(+)
> >>>
> >>> diff --git a/fs/io_uring.c b/fs/io_uring.c
> >>> index e96ed3d0385e..246f1085404d 100644
> >>> --- a/fs/io_uring.c
> >>> +++ b/fs/io_uring.c
> >>> @@ -2450,6 +2450,22 @@ static void io_req_task_submit(struct io_kiocb *req, bool *locked)
> >>>               io_req_complete_failed(req, -EFAULT);
> >>>  }
> >>>
> >>> +static void io_uring_cmd_work(struct io_kiocb *req, bool *locked)
> >>> +{
> >>> +     req->uring_cmd.driver_cb(&req->uring_cmd);
> >>
> >> If the callback memory area is gone, boom.
> > 
> > Why will the memory area be gone?
> > Module removal is protected because try_module_get is done anyway when
> > the namespace was opened.
> 
> And the req isn't going away before it's completed.

Just to be clear, I was thinking outside of the block layer context too.
Does this still hold true?

  Luis