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 4d34116842a66f88ec515e1218dd7360a77ccdf1..8eda897ec2a01aae7fd88e08d436e9ce4250822c 100644 (file)
--- 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);