• Wang YanQing's avatar
    tty: pty: Fix ldisc flush after userspace become aware of the data already · 77dae613
    Wang YanQing authored
    While using emacs, cat or others' commands in konsole with recent
    kernels, I have met many times that CTRL-C freeze konsole. After
    konsole freeze I can't type anything, then I have to open a new one,
    it is very annoying.
    See bug report:
    The platform in that bug report is Solaris, but now the pty in linux
    has the same problem or the same behavior as Solaris :)
    It has high possibility to trigger the problem follow steps below:
    Note: In my test, BigFile is a text file whose size is bigger than 1G
    1:open konsole
    1:cat BigFile
    After some digging, I find out the reason is that commit 1d1d14da
    ("pty: Fix buffer flush deadlock") changes the behavior of pty_flush_buffer.
    Thread A                                 Thread B
    --------                                 --------
    1:n_tty_poll return POLLIN
                                             2:CTRL-C trigger pty_flush_buffer
    3:attempt to check count of chars:
      ioctl(fd, TIOCINQ, &available)
      available is equal to 0
    4:read(fd, buffer, avaiable)
      return 0
    5:konsole close fd
    Yes, I know we could use the same patch included in the BUG report as
    a workaround for linux platform too. But I think the data in ldisc is
    belong to application of another side, we shouldn't clear it when we
    want to flush write buffer of this side in pty_flush_buffer. So I think
    it is better to disable ldisc flush in pty_flush_buffer, because its new
    hehavior bring no benefit except that it mess up the behavior between
    Also I find no flush_buffer function in others' tty driver has the
    same behavior as current pty_flush_buffer.
    Fixes: 1d1d14da ("pty: Fix buffer flush deadlock")
    CC: stable@vger.kernel.org # v4.0+
    Signed-off-by: default avatarWang YanQing <udknight@gmail.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
pty.c 22.2 KB