[PATCH 2/12] tty: Clarify disassociate_ctty

["Eric W. Biederman" <ebiederm@xmission.com>]

The code to look at tty_old_pgrp and send SIGHUP and SIGCONT
when it is present only executes when disassociate_ctty is
called from do_exit.  Make this clear by adding an explict
on_exit check, and explicitly setting tty_old_pgrp to 0.

In addition fix the locking by reading tty_old_pgrp under
the siglock.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
---
 drivers/char/tty_io.c |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index bb09e4a..acb2f5d 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -1508,8 +1508,12 @@ void disassociate_ctty(int on_exit)
 		/* XXX: here we race, there is nothing protecting tty */
 		if (on_exit && tty->driver->type != TTY_DRIVER_TYPE_PTY)
 			tty_vhangup(tty);
-	} else {
-		pid_t old_pgrp = current->signal->tty_old_pgrp;
+	} else if (on_exit) {
+		pid_t old_pgrp;
+		spin_lock_irq(&current->sighand->siglock);
+		old_pgrp = current->signal->tty_old_pgrp;
+		current->signal->tty_old_pgrp = 0;
+		spin_unlock_irq(&current->sighand->siglock);
 		if (old_pgrp) {
 			kill_pg(old_pgrp, SIGHUP, on_exit);
 			kill_pg(old_pgrp, SIGCONT, on_exit);
-- 
1.4.4.1.g278f