tty: revert incorrectly applied lock patch

I sent GregKH this after the pre-requisites. He dropped the pre-requesites
for good reason and unfortunately then applied this patch. Without this
reverted you get random kernel memory corruption which will make bisecting
anything between it and the properly applied patches a complete sod.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 29 insertions, 38 deletions

diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index 847f7ed7a3ed..6f99c9959f0c 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -568,7 +568,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
         if (IS_ERR(new_ldisc))
                 return PTR_ERR(new_ldisc);
 
-        tty_lock(tty);
+        tty_lock();
         /*
          *      We need to look at the tty locking here for pty/tty pairs
          *      when both sides try to change in parallel.
@@ -582,12 +582,12 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
          */
 
         if (tty->ldisc->ops->num == ldisc) {
-                tty_unlock(tty);
+                tty_unlock();
                 tty_ldisc_put(new_ldisc);
                 return 0;
         }
 
-        tty_unlock(tty);
+        tty_unlock();
         /*
          *      Problem: What do we do if this blocks ?
          *      We could deadlock here
@@ -595,7 +595,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 
         tty_wait_until_sent(tty, 0);
 
-        tty_lock(tty);
+        tty_lock();
         mutex_lock(&tty->ldisc_mutex);
 
         /*
@@ -605,10 +605,10 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 
         while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
                 mutex_unlock(&tty->ldisc_mutex);
-                tty_unlock(tty);
+                tty_unlock();
                 wait_event(tty_ldisc_wait,
                         test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
-                tty_lock(tty);
+                tty_lock();
                 mutex_lock(&tty->ldisc_mutex);
         }
 
@@ -623,7 +623,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 
         o_ldisc = tty->ldisc;
 
-        tty_unlock(tty);
+        tty_unlock();
         /*
          *      Make sure we don't change while someone holds a
          *      reference to the line discipline. The TTY_LDISC bit
@@ -650,7 +650,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 
         retval = tty_ldisc_wait_idle(tty, 5 * HZ);
 
-        tty_lock(tty);
+        tty_lock();
         mutex_lock(&tty->ldisc_mutex);
 
         /* handle wait idle failure locked */
@@ -665,7 +665,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
                 clear_bit(TTY_LDISC_CHANGING, &tty->flags);
                 mutex_unlock(&tty->ldisc_mutex);
                 tty_ldisc_put(new_ldisc);
-                tty_unlock(tty);
+                tty_unlock();
                 return -EIO;
         }
 
@@ -708,7 +708,7 @@ enable:
         if (o_work)
                 schedule_work(&o_tty->buf.work);
         mutex_unlock(&tty->ldisc_mutex);
-        tty_unlock(tty);
+        tty_unlock();
         return retval;
 }
 
@@ -816,11 +816,11 @@ void tty_ldisc_hangup(struct tty_struct *tty)
          * need to wait for another function taking the BTM
          */
         clear_bit(TTY_LDISC, &tty->flags);
-        tty_unlock(tty);
+        tty_unlock();
         cancel_work_sync(&tty->buf.work);
         mutex_unlock(&tty->ldisc_mutex);
 retry:
-        tty_lock(tty);
+        tty_lock();
         mutex_lock(&tty->ldisc_mutex);
 
         /* At this point we have a closed ldisc and we want to
@@ -831,7 +831,7 @@ retry:
                 if (atomic_read(&tty->ldisc->users) != 1) {
                         char cur_n[TASK_COMM_LEN], tty_n[64];
                         long timeout = 3 * HZ;
-                        tty_unlock(tty);
+                        tty_unlock();
 
                         while (tty_ldisc_wait_idle(tty, timeout) == -EBUSY) {
                                 timeout = MAX_SCHEDULE_TIMEOUT;
@@ -894,23 +894,6 @@ int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
         tty_ldisc_enable(tty);
         return 0;
 }
-
-static void tty_ldisc_kill(struct tty_struct *tty)
-{
-        mutex_lock(&tty->ldisc_mutex);
-        /*
-         * Now kill off the ldisc
-         */
-        tty_ldisc_close(tty, tty->ldisc);
-        tty_ldisc_put(tty->ldisc);
-        /* Force an oops if we mess this up */
-        tty->ldisc = NULL;
-
-        /* Ensure the next open requests the N_TTY ldisc */
-        tty_set_termios_ldisc(tty, N_TTY);
-        mutex_unlock(&tty->ldisc_mutex);
-}
-
 /**
  *      tty_ldisc_release               -       release line discipline
  *      @tty: tty being shut down
@@ -929,19 +912,27 @@ void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
          * race with the set_ldisc code path.
          */
 
-        tty_unlock_pair(tty, o_tty);
+        tty_unlock();
         tty_ldisc_halt(tty);
         tty_ldisc_flush_works(tty);
-        if (o_tty) {
-                tty_ldisc_halt(o_tty);
-                tty_ldisc_flush_works(o_tty);
-        }
-        tty_lock_pair(tty, o_tty);
+        tty_lock();
 
+        mutex_lock(&tty->ldisc_mutex);
+        /*
+         * Now kill off the ldisc
+         */
+        tty_ldisc_close(tty, tty->ldisc);
+        tty_ldisc_put(tty->ldisc);
+        /* Force an oops if we mess this up */
+        tty->ldisc = NULL;
+
+        /* Ensure the next open requests the N_TTY ldisc */
+        tty_set_termios_ldisc(tty, N_TTY);
+        mutex_unlock(&tty->ldisc_mutex);
 
-        tty_ldisc_kill(tty);
+        /* This will need doing differently if we need to lock */
         if (o_tty)
-                tty_ldisc_kill(o_tty);
+                tty_ldisc_release(o_tty, NULL);
 
         /* And the memory resources remaining (buffers, termios) will be
            disposed of when the kref hits zero */