From: Peter Hurley <peter@hurleysoftware.com>
Date: Sun, 10 Jan 2016 05:13:45 +0000 (-0800)
Subject: tty: Retry failed reopen if tty teardown in-progress
X-Git-Tag: firefly_0821_release~3391^2~45
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=b4312250147d42dceed6c8d44aa02cb29539db19;p=firefly-linux-kernel-4.4.55.git

tty: Retry failed reopen if tty teardown in-progress

commit 7f22f6c935cda600660e623a411fe380015d28d9 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 4d34116842a6..8eda897ec2a0 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1462,13 +1462,13 @@ 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;
 
@@ -2092,7 +2092,11 @@ 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);