| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.11 100/114] tty: pty: Fix ldisc flush after userspace become aware of the data already | Date | Thu, 18 May 2017 12:46:50 +0200 |
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4.11-stable review patch. If anyone has any objections, please let me know.
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From: Wang YanQing <udknight@gmail.com>
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") Signed-off-by: Wang YanQing <udknight@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- drivers/tty/pty.c | 7 +------ 1 file changed, 1 insertion(+), 6 deletions(-)
--- a/drivers/tty/pty.c +++ b/drivers/tty/pty.c @@ -216,16 +216,11 @@ static int pty_signal(struct tty_struct 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;
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