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

[Jens Axboe <axboe@kernel.dk>]

On 3/16/24 10:57 AM, Pavel Begunkov wrote:
> On 3/16/24 16:51, Jens Axboe wrote:
>> On 3/16/24 10:46 AM, Pavel Begunkov wrote:
>>> On 3/16/24 16:42, Jens Axboe wrote:
>>>> On 3/16/24 10:36 AM, Pavel Begunkov wrote:
>>>>> On 3/16/24 16:36, Jens Axboe wrote:
>>>>>> On 3/16/24 10:32 AM, Pavel Begunkov wrote:
>>>>>>> On 3/16/24 16:31, Jens Axboe wrote:
>>>>>>>> On 3/16/24 10:28 AM, Pavel Begunkov wrote:
>>>>>>>>> On 3/16/24 16:14, Jens Axboe wrote:
>>>>>>>>>> On 3/15/24 5:28 PM, Pavel Begunkov wrote:
>>>>>>>>>>> On 3/15/24 23:25, Jens Axboe wrote:
>>>>>>>>>>>> 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?
>>>>>>>>>>>
>>>>>>>>>>> I'd rather leave it to you, I suspect it wouldn't fix the syzbot
>>>>>>>>>>> report w/o fiddling with done_io as in your patch.
>>>>>>>>>>
>>>>>>>>>> I gave this a shot, but some fail handlers do want to get called. But
>>>>>>>>>
>>>>>>>>> Which one and/or which part of it?
>>>>>>>>
>>>>>>>> send zc
>>>>>>>
>>>>>>> I don't think so. If prep wasn't called there wouldn't be
>>>>>>> a notif allocated, and so no F_MORE required. If you take
>>>>>>> at the code path it's under REQ_F_NEED_CLEANUP, which is only
>>>>>>> set by opcode handlers
>>>>>>
>>>>>> I'm not making this up, your test case will literally fail as it doesn't
>>>>>> get to flag MORE for that case. FWIW, this was done with EARLY_FAIL
>>>>>> being flagged, and failing if we fail during or before prep.
>>>>>
>>>>> Maybe the test is too strict, but your approach is different
>>>>> from what I mentioned yesterday
>>>>>
>>>>> -    return def->prep(req, sqe);
>>>>> +    ret = def->prep(req, sqe);
>>>>> +    if (unlikely(ret)) {
>>>>> +        req->flags |= REQ_F_EARLY_FAIL;
>>>>> +        return ret;
>>>>> +    }
>>>>> +
>>>>> +    return 0;
>>>>>
>>>>> It should only set REQ_F_EARLY_FAIL if we fail
>>>>> _before_ prep is called
>>>>
>>>> I did try both ways, fails if we just have:
>>>
>>> Ok, but the point is that the sendzc's ->fail doesn't
>>> need to be called unless you've done ->prep first.
>>
>> But it fails, not sure how else to say it.
> 
> liburing tests? Which test case? If so, it should be another

Like I mentioned earlier, it's send zc and it's failing the test case
for that. test/send-zerocopy.t.

> bug. REQ_F_NEED_CLEANUP is only set by opcodes, if a request is
> terminated before ->prep is called, it means it never entered
> any of the opdef callbacks and have never seen any of net.c
> code, so there should be no REQ_F_NEED_CLEANUP, and so
> io_sendrecv_fail() wouldn't try to set F_MORE. I don't know
> what's wrong.

Feel free to take a look! I do like the simplicity of the early error
flag.

-- 
Jens Axboe