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

[Jens Axboe <axboe@kernel.dk>]

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
they can't use sr->done_io at that point. I'll ponder this a bit and see
what the best generic solution is.

-- 
Jens Axboe