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

[Jens Axboe <axboe@kernel.dk>]

On 2/17/22 11:46 AM, Luis Chamberlain wrote:
> 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?

It has nothing to do with the block layer, the req belongs to io_uring
context. io_uring has ownership of it.

-- 
Jens Axboe