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

[Jens Axboe <axboe@kernel.dk>]

On 3/16/24 11:42 AM, Pavel Begunkov wrote:
> On 3/16/24 17:01, Jens Axboe wrote:
>> 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.
> 
> ./send-zerocopy.t works fine

Huh, I wonder what I messed up. But:

> @@ -2250,7 +2249,13 @@ 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)) {
> +        req->flags |= REQ_F_UNPREPPED_FAIL;
> +        return io_submit_fail_init(sqe, req, ret);
> +    }
> +
> +    ret = def->prep(req, sqe);
> +    if (ret)
>          return io_submit_fail_init(sqe, req, ret);

this obviously won't compile, assuming this is not the one you ran.

In any case, I do like the one I sent out for review. It moves all the
slow path out of line and shrinks things nicely too. And clearing the
cmd.data area seems like a good idea for that case.

-- 
Jens Axboe