Messages in this thread Patch in this message | | | Date | Wed, 8 May 2013 02:47:34 +0800 | From | Wang YanQing <> | Subject | [PATCH]TTY: Fix tty can't be restarted by TCXONC ioctl request |
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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); } -- 1.7.12.4.dirty
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