patch "tty: Retry failed reopen if tty teardown in-progress" added to tty-next

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    tty: Retry failed reopen if tty teardown in-progress

to my tty git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
in the tty-next branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will also be merged in the next major kernel release
during the merge window.

If you have any questions about this process, please let me know.


>From 7f22f6c935cda600660e623a411fe380015d28d9 Mon Sep 17 00:00:00 2001
From: Peter Hurley <peter@hurleysoftware.com>
Date: Sat, 9 Jan 2016 21:13:45 -0800
Subject: tty: Retry failed reopen if tty teardown in-progress

A small window exists where a tty reopen will observe the tty
just prior to imminent teardown (tty->count == 0); in this case, open()
returns EIO to userspace.

Instead, retry the open after checking for signals and yielding;
this interruptible retry loop allows teardown to commence and initialize
a new tty on retry. Never retry the BSD master pty reopen; there is no
guarantee the pty pair teardown is imminent since the slave file
descriptors may remain open indefinitely.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Cc: stable <stable@vger.kernel.org> # 4.4
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/tty/tty_io.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 765935b144d6..a1b36bf545e8 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1463,13 +1463,13 @@ static int tty_reopen(struct tty_struct *tty)
 {
 	struct tty_driver *driver = tty->driver;
 
-	if (!tty->count)
-		return -EIO;
-
 	if (driver->type == TTY_DRIVER_TYPE_PTY &&
 	    driver->subtype == PTY_TYPE_MASTER)
 		return -EIO;
 
+	if (!tty->count)
+		return -EAGAIN;
+
 	if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN))
 		return -EBUSY;
 
@@ -2088,7 +2088,11 @@ retry_open:
 
 	if (IS_ERR(tty)) {
 		retval = PTR_ERR(tty);
-		goto err_file;
+		if (retval != -EAGAIN || signal_pending(current))
+			goto err_file;
+		tty_free_file(filp);
+		schedule();
+		goto retry_open;
 	}
 
 	tty_add_file(tty, filp);
-- 
2.7.0