tty: Remove unnecessary re-test of ldisc ref count

Since the tty->ldisc is prevented from being changed by tty_set_ldisc()
when a tty is being hung up, re-testing the ldisc user count is
unnecessary -- ie, it cannot be a different ldisc and the user count
cannot have increased (assuming the caller meets the precondition that
TTY_LDISC flag is cleared)

Removal of the 'early-out' locking optimization is necessary for
the subsequent patch 'tty: Fix ldisc halt sequence on hangup'.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index c5b848a78e49fe71970573096ba03523207784ba..fa0170e1b08287bdea777ea952749f5c9998a9c5 100644 (file)
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -558,29 +558,29 @@ static int tty_ldisc_wait_idle(struct tty_struct *tty, long timeout)
  *     have been halted for this to guarantee it remains idle.
  *
  *     Caller must hold legacy and ->ldisc_mutex.
+ *
+ *     NB: tty_set_ldisc() is prevented from changing the ldisc concurrently
+ *     with this function by checking the TTY_HUPPING flag.
  */
 static bool tty_ldisc_hangup_wait_idle(struct tty_struct *tty)
 {
-       while (tty->ldisc) {    /* Not yet closed */
-               if (atomic_read(&tty->ldisc->users) != 1) {
-                       char cur_n[TASK_COMM_LEN], tty_n[64];
-                       long timeout = 3 * HZ;
-                       tty_unlock(tty);
-
-                       while (tty_ldisc_wait_idle(tty, timeout) == -EBUSY) {
-                               timeout = MAX_SCHEDULE_TIMEOUT;
-                               printk_ratelimited(KERN_WARNING
-                                       "%s: waiting (%s) for %s took too long, but we keep waiting...\n",
-                                       __func__, get_task_comm(cur_n, current),
-                                       tty_name(tty, tty_n));
-                       }
-                       /* must reacquire both locks and preserve lock order */
-                       mutex_unlock(&tty->ldisc_mutex);
-                       tty_lock(tty);
-                       mutex_lock(&tty->ldisc_mutex);
-                       continue;
+       char cur_n[TASK_COMM_LEN], tty_n[64];
+       long timeout = 3 * HZ;
+
+       if (tty->ldisc) {       /* Not yet closed */
+               tty_unlock(tty);
+
+               while (tty_ldisc_wait_idle(tty, timeout) == -EBUSY) {
+                       timeout = MAX_SCHEDULE_TIMEOUT;
+                       printk_ratelimited(KERN_WARNING
+                               "%s: waiting (%s) for %s took too long, but we keep waiting...\n",
+                               __func__, get_task_comm(cur_n, current),
+                               tty_name(tty, tty_n));
                }
-               break;
+               /* must reacquire both locks and preserve lock order */
+               mutex_unlock(&tty->ldisc_mutex);
+               tty_lock(tty);
+               mutex_lock(&tty->ldisc_mutex);
        }
        return !!tty->ldisc;
 }