Re: [PATCH v2] io_uring/net: ensure async prep handlers always initialize ->done_io

[Jens Axboe <axboe@kernel.dk>]

On 3/15/24 5:19 PM, Pavel Begunkov wrote:
> On 3/15/24 23:13, Pavel Begunkov wrote:
>> On 3/15/24 23:09, Pavel Begunkov wrote:
>>> On 3/15/24 22:48, Jens Axboe wrote:
>>>> If we get a request with IOSQE_ASYNC set, then we first run the prep
>>>> async handlers. But if we then fail setting it up and want to post
>>>> a CQE with -EINVAL, we use ->done_io. This was previously guarded with
>>>> REQ_F_PARTIAL_IO, and the normal setup handlers do set it up before any
>>>> potential errors, but we need to cover the async setup too.
>>>
>>> You can hit io_req_defer_failed() { opdef->fail(); }
>>> off of an early submission failure path where def->prep has
>>> not yet been called, I don't think the patch will fix the
>>> problem.
>>>
>>> ->fail() handlers are fragile, maybe we should skip them
>>> if def->prep() wasn't called. Not even compile tested:
>>>
>>>
>>> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
>>> index 846d67a9c72e..56eed1490571 100644
>>> --- a/io_uring/io_uring.c
>>> +++ b/io_uring/io_uring.c
> [...]
>>>           def->fail(req);
>>>       io_req_complete_defer(req);
>>>   }
>>> @@ -2201,8 +2201,7 @@ static int io_init_req(struct io_ring_ctx *ctx, struct io_kiocb *req,
>>>           }
>>>           req->flags |= REQ_F_CREDS;
>>>       }
>>> -
>>> -    return def->prep(req, sqe);
>>> +    return 0;
>>>   }
>>>
>>>   static __cold int io_submit_fail_init(const struct io_uring_sqe *sqe,
>>> @@ -2250,8 +2249,15 @@ static inline int io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
>>>       int ret;
>>>
>>>       ret = io_init_req(ctx, req, sqe);
>>> -    if (unlikely(ret))
>>> +    if (unlikely(ret)) {
>>> +fail:
> 
> Obvious the diff is crap, but still bugging me enough to write
> that the label should've been one line below, otherwise we'd
> flag after ->prep as well.

It certainly needs testing :-)

We can go either way - patch up the net thing, or do a proper EARLY_FAIL
and hopefully not have to worry about it again. Do you want to clean it
up, test it, and send it out?

-- 
Jens Axboe