Messages in this thread | | | Date | Tue, 07 May 2013 16:50:05 -0400 | From | Peter Hurley <> | Subject | Re: [PATCH]TTY: Fix tty can't be restarted by TCXONC ioctl request |
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On 05/07/2013 02:47 PM, Wang YanQing wrote: > I meet emacs hang in start if I do the operation below: > 1: echo 3 > /proc/sys/vm/drop_caches > 2: emacs BigFile > 3: Press CTRL-S follow 2 immediately > > Then emacs hang on, CTRL-Q can't resume, the terminal > hang on, you can do nothing with this terminal except > close it. > > The reason is before emacs takeover control the tty, > we use CTRL-S to XOFF it. Then when emacs takeover the > control, it may don't use the flow-control, so emacs hang. > But after search the emacs's startup codes, I find they use TCXONC > to workaround this situation: > > /* This code added to insure that, if flow-control is not to be used, > we have an unlocked terminal at the start. */ > if (!tty_out->flow_control) ioctl (fileno (tty_out->input), TCXONC, 1); > ioctl (fileno (tty_out->input), TCXONC, 1); > > But this workaround never work due the kernel's current code. > This patch fix it. > > Below is the ChangeLog introduce the tty->flow_stopped flag: > > Thu Nov 21 10:05:22 1996 Theodre Ts'o <tytso@localhost.mit.edu> > > * tty_ioctl.c (tty_wait_until_sent): Always check the driver > wait_until_ready routine, even if there are no characters > in the xmit buffer. (There may be charactes in the device > FIFO.) > (n_tty_ioctl): Add new flag tty->flow_stopped which > indicates whether the tty is stopped due to a request by > the TCXONC ioctl (used by tcflow). If so, don't let an > incoming XOFF character restart the tty. The tty can only > be restarted by another TCXONC request. > > So I think this patch make TCXONC can restart tty which stopped by > STOP_CHAR don't break the original meaning. > > This patch will fix some strange tty relation hang problem, > I believe I meet it with vim in ssh, and also see below bug report: > http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=465823 > > Signed-off-by: Wang YanQing <udknight@gmail.com> > --- > drivers/tty/tty_ioctl.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c > index e4455e0..42e08e5 100644 > --- a/drivers/tty/tty_ioctl.c > +++ b/drivers/tty/tty_ioctl.c > @@ -1129,11 +1129,12 @@ int n_tty_ioctl_helper(struct tty_struct *tty, struct file *file, > case TCOOFF: > if (!tty->flow_stopped) { > tty->flow_stopped = 1; > - stop_tty(tty); > + if (!tty->stopped) > + stop_tty(tty); > } > break; > case TCOON: > - if (tty->flow_stopped) { > + if (tty->flow_stopped || tty->stopped) { > tty->flow_stopped = 0; > start_tty(tty); > }
This should be fixed in n_tty_set_termios() instead of fixing userspace workarounds.
The problem occurs when the tty has been stopped with STOP_CHAR(tty) and then termios is changed so that START_CHAR(tty) is subsequently ignored (in the reported case, I_IXON(tty) is cleared).
Regards, Peter Hurley
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