Re: [PATCH 1/2] io_uring/uring_cmd: cleanup struct io_uring_cmd_data layout

[Jens Axboe <axboe@kernel.dk>]

On 1/23/25 7:57 AM, Pavel Begunkov wrote:
> On 1/23/25 14:54, Jens Axboe wrote:
>> On 1/23/25 7:38 AM, Pavel Begunkov wrote:
>>> On 1/23/25 14:21, Jens Axboe wrote:
>>>> A few spots in uring_cmd assume that the SQEs copied are always at the
>>>> start of the structure, and hence mix req->async_data and the struct
>>>> itself.
>>>>
>>>> Clean that up and use the proper indices.
>>>>
>>>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>>> ---
>>>>    io_uring/uring_cmd.c | 6 +++---
>>>>    1 file changed, 3 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
>>>> index 3993c9339ac7..6a63ec4b5445 100644
>>>> --- a/io_uring/uring_cmd.c
>>>> +++ b/io_uring/uring_cmd.c
>>>> @@ -192,8 +192,8 @@ static int io_uring_cmd_prep_setup(struct io_kiocb *req,
>>>>            return 0;
>>>>        }
>>>>    -    memcpy(req->async_data, sqe, uring_sqe_size(req->ctx));
>>>> -    ioucmd->sqe = req->async_data;
>>>> +    memcpy(cache->sqes, sqe, uring_sqe_size(req->ctx));
>>>> +    ioucmd->sqe = cache->sqes;
>>>>        return 0;
>>>>    }
>>>>    @@ -260,7 +260,7 @@ int io_uring_cmd(struct io_kiocb *req, unsigned int issue_flags)
>>>>            struct io_uring_cmd_data *cache = req->async_data;
>>>>              if (ioucmd->sqe != (void *) cache)
>>>> -            memcpy(cache, ioucmd->sqe, uring_sqe_size(req->ctx));
>>>> +            memcpy(cache->sqes, ioucmd->sqe, uring_sqe_size(req->ctx));
>>>
>>> 3347fa658a1b ("io_uring/cmd: add per-op data to struct io_uring_cmd_data")
>>>
>>> IIUC the patch above is queued for 6.14, and with that this patch
>>> looks like a fix? At least it feels pretty dangerous without.
>>
>> It's not a fix, the sqes are first in the struct even with that patch.
> 
> Ah yes
> 
>> So I'd consider it a cleanup. In any case, targeting 6.14 for these
>> alloc cache cleanups as it got introduced there as well.
> 
> That's good, makes it not that brittle

Yep it was too easy to miss, don't like them being aliased like that
even if the usage was currently fine.

-- 
Jens Axboe