| From 77dae6134440420bac334581a3ccee94cee1c054 Mon Sep 17 00:00:00 2001 |
| From: Wang YanQing <udknight@gmail.com> |
| Date: Wed, 22 Feb 2017 19:37:08 +0800 |
| Subject: [PATCH] tty: pty: Fix ldisc flush after userspace become aware of the |
| data already |
| |
| commit 77dae6134440420bac334581a3ccee94cee1c054 upstream. |
| |
| 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: |
| https://bugs.kde.org/show_bug.cgi?id=175283 |
| |
| 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 |
| 2:CTRL-C |
| |
| After some digging, I find out the reason is that commit 1d1d14da12e7 |
| ("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 |
| tty_buffer_flush |
| n_tty_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 |
| POLLIN, and TIOCINQ or FIONREAD. |
| |
| Also I find no flush_buffer function in others' tty driver has the |
| same behavior as current pty_flush_buffer. |
| |
| Fixes: 1d1d14da12e7 ("pty: Fix buffer flush deadlock") |
| CC: stable@vger.kernel.org # v4.0+ |
| Signed-off-by: Wang YanQing <udknight@gmail.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c |
| index 66b59a15780d..65799575c666 100644 |
| --- a/drivers/tty/pty.c |
| +++ b/drivers/tty/pty.c |
| @@ -216,16 +216,11 @@ static int pty_signal(struct tty_struct *tty, int sig) |
| static void pty_flush_buffer(struct tty_struct *tty) |
| { |
| struct tty_struct *to = tty->link; |
| - struct tty_ldisc *ld; |
| |
| if (!to) |
| return; |
| |
| - ld = tty_ldisc_ref(to); |
| - tty_buffer_flush(to, ld); |
| - if (ld) |
| - tty_ldisc_deref(ld); |
| - |
| + tty_buffer_flush(to, NULL); |
| if (to->packet) { |
| spin_lock_irq(&tty->ctrl_lock); |
| tty->ctrl_status |= TIOCPKT_FLUSHWRITE; |
| -- |
| 2.12.0 |
| |
