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authorWang YanQing <udknight@gmail.com>2017-02-22 11:37:08 (GMT)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-05-20 12:28:41 (GMT)
commit89c91ea375816c2a34c4035c7feb40db3f053ae9 (patch)
tree148fa42b9166cdd8a651bea45b85493d43cab962 /drivers/tty
parente38a4c3b0b4a3df1abbe7ae9c175eed62286f963 (diff)
downloadlinux-89c91ea375816c2a34c4035c7feb40db3f053ae9.tar.xz
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") Signed-off-by: Wang YanQing <udknight@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty')
-rw-r--r--drivers/tty/pty.c7
1 files changed, 1 insertions, 6 deletions
diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index a23fa5e..2b90738 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;