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>

1 files changed, 19 insertions, 19 deletions

diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index c5b848a78e49..fa0170e1b082 100644
--- 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;
 }