> test_subprocess_interactive (test.test_asyncio.test_events.PollEventLoopTests) ... 
> 4588380:        64422135: close(3)                              = 0
> 4588380:        64422135: statx("/home/dje/src/cpython/Lib/test/test_asyncio/echo.py", 0x2FF20870, 128, 010) = 0
> 4588380:        64422135: kopen("/home/dje/src/cpython/Lib/test/test_asyncio/echo.py", O_RDONLY|O_LARGEFILE) = 3
> 4588380:        64422135: kioctl(3, 22528, 0x00000000, 0x00000000) Err#25 ENOTTY
> 4588380:        64422135: kfcntl(3, F_SETFD, 0x00000001)        = 0
> 4588380:        64422135: fstatx(0x00000003, 0x2FF229E8, 0x00000080, 0x00000008) = 0x00000000
> 4588380:        64422135: kioctl(3, 22528, 0x00000000, 0x00000000) Err#25 ENOTTY
> 4588380:        64422135: lseek(0x00000003, 0x00000000, 0x00000001) = 0x00000000
> 4588380:        64422135: kioctl(3, 22528, 0x00000000, 0x00000000) Err#25 ENOTTY
> 4588380:        64422135: kread(3, " i m p o r t   o s\n\n i".., 4096) = 110
> 4588380:        64422135: klseek(3, 4294967295, -108, 0x00000001) = 0
> 4588380:        64422135: klseek(3, 0, 0, 0x00000000)           = 0
> 4588380:        64422135: kread(3, " i m p o r t   o s\n\n i".., 4096) = 110
> 4588380:        64422135: kread(3, " i m p o r t   o s\n\n i".., 4096) = 0
> 4588380:        64422135: close(3)                              = 0
> 4588380:        64422135: kread(0, " P y t h o n   � � � � �".., 1024) = 7
> 4588380:        64422135: kwrite(0x00000001, 0x200CD0A0, 0x00000007) = 0x00000007
> 4588380:             0x00000000: " P y t h o n   � � � � �"..
> 59244954: 33161535: _poll(0x2067A970, 3, -1)            = 1
> 4588380:        64422135: kread(0, " � � � � � � � � � � � �".., 1024) = 0
> 4588380:        64422135: kwrite(0x00000001, 0x200CD0F0, 0x00000000) = 0x00000000
> 4588380:             0x00000000: " � � � � � � � � � � � �"..

It seems echo.py should at least exit on EOF, which would prevent the
hangs (right now it's stuck in a busy loop calling os.read(0) which
always returns immediately).

(same for echo3.py)