Re: [PATCH] io_uring: fix blocking inline submission

[Jens Axboe <axboe@kernel.dk>]

On 6/9/21 5:07 AM, Pavel Begunkov wrote:
> There is a complaint against sys_io_uring_enter() blocking if it submits
> stdin reads. The problem is in __io_file_supports_async(), which
> sees that it's a cdev and allows it to be processed inline.
> 
> Punt char devices using generic rules of io_file_supports_async(),
> including checking for presence of *_iter() versions of rw callbacks.
> Apparently, it will affect most of cdevs with some exceptions like
> null and zero devices.

I don't like this, we really should fix the file types, they are
broken if they don't honor IOCB_NOWAIT and have ->read_iter() (or
the write equiv).

For cases where there is no iter variant of the read/write handlers,
then yes we should not return true from __io_file_supports_async().

-- 
Jens Axboe