This is a note to let you know that I've just added the patch titled
tty: pty: Fix ldisc flush after userspace become aware of the data already
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tty-pty-fix-ldisc-flush-after-userspace-become-aware-of-the-data-already.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 77dae6134440420bac334581a3ccee94cee1c054 Mon Sep 17 00:00:00 2001
From: Wang YanQing <udknight@xxxxxxxxx>
Date: Wed, 22 Feb 2017 19:37:08 +0800
Subject: tty: pty: Fix ldisc flush after userspace become aware of the data already
From: Wang YanQing <udknight@xxxxxxxxx>
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@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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;
Patches currently in stable-queue which might be from udknight@xxxxxxxxx are
queue-4.4/tty-pty-fix-ldisc-flush-after-userspace-become-aware-of-the-data-already.patch