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

[Pavel Begunkov <asml.silence@gmail.com>]

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.


> 	return def->prep(req, sqe);
> fail:
> 	req->flags |= REQ_F_EARLY_FAIL;
> 	...
> 
> as well.
> 

-- 
Pavel Begunkov