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

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

On 3/16/24 16:51, 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
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.


> FWIW, the current io_uring-6.9 branch has two patches on top, looks fine
> for me so far. We'll see if syzbot agrees. I'll send them out later
> today, unless I change my mind and try a different approach.
> 

-- 
Pavel Begunkov