On 6/9/21 4:43 PM, Jens Axboe wrote: > On 6/9/21 9:41 AM, Pavel Begunkov wrote: >> On 6/9/21 4:36 PM, Jens Axboe wrote: >>> On 6/9/21 9:34 AM, Pavel Begunkov wrote: >>>> 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. >>> >>> Ah ok, yes then that is indeed fine. >>> >>>> 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. >>> >>> I think they do, but they don't honor IOCB_NOWAIT for example. I'd >>> be curious if the patch actually fixes the reported case, even though >>> it is most likely the right thing to do. If not, then the fops handler >>> need fixing for that driver. >> >> Yep, weird, but fixes it for me. A simple repro was attached >> to the issue. >> >> https://github.com/axboe/liburing/issues/354 > > Ah ok, all good then for now. I have applied the patch, and added > the reported-by as well. Great, thanks. Will check what's with the tty part -- Pavel Begunkov
