tty: disassociate_ctty() sends the extra SIGCONT

Starting from v3.10 (probably commit f91e2590410b: "tty: Signal
foreground group processes in hangup") disassociate_ctty() sends SIGCONT
if tty && on_exit.  This breaks LSB test-suite, in particular test8 in
_exit.c and test40 in sigcon5.c.

Put the "!on_exit" check back to restore the old behaviour.

Review by Peter Hurley:
 "Yes, this regression was introduced by me in that commit.  The effect
  of the regression is that ptys will receive a SIGCONT when, in similar
  circumstances, ttys would not.

  The fact that two test vectors accidentally tripped over this
  regression suggests that some other apps may as well.

  Thanks for catching this"

Cc: stable@vger.kernel.org # v3.10+
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Karel Srot <ksrot@redhat.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index a9355ce1c6d5..3a1a01af9a80 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -854,7 +854,8 @@ void disassociate_ctty(int on_exit)
                         struct pid *tty_pgrp = tty_get_pgrp(tty);
                         if (tty_pgrp) {
                                 kill_pgrp(tty_pgrp, SIGHUP, on_exit);
-                                kill_pgrp(tty_pgrp, SIGCONT, on_exit);
+                                if (!on_exit)
+                                        kill_pgrp(tty_pgrp, SIGCONT, on_exit);
                                 put_pid(tty_pgrp);
                         }
                 }