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

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

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.

-- 
Pavel Begunkov