On 6/9/21 4:07 PM, Jens Axboe wrote: > 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(). I'm confused. The patch doesn't punt them unconditionally, but make it go through the generic path of __io_file_supports_async() including checks for read_iter/write_iter. So if a chrdev has *_iter() it should continue to work as before. It fixes the symptom that means the change punts it async, and so I assume tty doesn't have _iter()s for some reason. Will take a look at the tty driver soon to stop blind guessing. -- Pavel Begunkov
