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

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

On 3/15/24 23:13, 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.


>> +        req->flags |= REQ_F_EARLY_FAIL;
>>           return io_submit_fail_init(sqe, req, ret);
>> +    }
>> +
>> +    ret = def->prep(req, sqe);
>> +    if (unlikely(ret))
>> +        goto fail;
>>
>>       trace_io_uring_submit_req(req);
>>
> 

-- 
Pavel Begunkov