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. -- Jens Axboe
