[PATCH 4.4 075/117] tty: Retry failed reopen if tty teardown in-progress

Greg Kroah-Hartman
2016-02-15T00:30:49Z

From: Peter Hurley <peter@hurleysoftware.com>

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>

---
drivers/tty/tty_io.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1462,13 +1462,13 @@ static int tty_reopen(struct tty_struct
{
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);