2 files changed, 54 insertions, 100 deletions

diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c
index acd76b767d4c..1733d3439ad2 100644
--- a/drivers/char/tty_ldisc.c
+++ b/drivers/char/tty_ldisc.c
@@ -48,6 +48,41 @@ static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
 /* Line disc dispatch table */
 static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
 
+static inline struct tty_ldisc *get_ldisc(struct tty_ldisc *ld)
+{
+        if (ld)
+                atomic_inc(&ld->users);
+        return ld;
+}
+
+static void put_ldisc(struct tty_ldisc *ld)
+{
+        unsigned long flags;
+
+        if (WARN_ON_ONCE(!ld))
+                return;
+
+        /*
+         * If this is the last user, free the ldisc, and
+         * release the ldisc ops.
+         *
+         * We really want an "atomic_dec_and_lock_irqsave()",
+         * but we don't have it, so this does it by hand.
+         */
+        local_irq_save(flags);
+        if (atomic_dec_and_lock(&ld->users, &tty_ldisc_lock)) {
+                struct tty_ldisc_ops *ldo = ld->ops;
+
+                ldo->refcount--;
+                module_put(ldo->owner);
+                spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+
+                kfree(ld);
+                return;
+        }
+        local_irq_restore(flags);
+}
+
 /**
  *      tty_register_ldisc      -       install a line discipline
  *      @disc: ldisc number
@@ -142,7 +177,7 @@ static struct tty_ldisc *tty_ldisc_try_get(int disc)
                         /* lock it */
                         ldops->refcount++;
                         ld->ops = ldops;
-                        ld->refcount = 0;
+                        atomic_set(&ld->users, 1);
                         err = 0;
                 }
         }
@@ -181,35 +216,6 @@ static struct tty_ldisc *tty_ldisc_get(int disc)
         return ld;
 }
 
-/**
- *      tty_ldisc_put           -       drop ldisc reference
- *      @ld: ldisc
- *
- *      Drop a reference to a line discipline. Manage refcounts and
- *      module usage counts. Free the ldisc once the recount hits zero.
- *
- *      Locking:
- *              takes tty_ldisc_lock to guard against ldisc races
- */
-
-static void tty_ldisc_put(struct tty_ldisc *ld)
-{
-        unsigned long flags;
-        int disc = ld->ops->num;
-        struct tty_ldisc_ops *ldo;
-
-        BUG_ON(disc < N_TTY || disc >= NR_LDISCS);
-
-        spin_lock_irqsave(&tty_ldisc_lock, flags);
-        ldo = tty_ldiscs[disc];
-        BUG_ON(ldo->refcount == 0);
-        ldo->refcount--;
-        module_put(ldo->owner);
-        spin_unlock_irqrestore(&tty_ldisc_lock, flags);
-        WARN_ON(ld->refcount);
-        kfree(ld);
-}
-
 static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
 {
         return (*pos < NR_LDISCS) ? pos : NULL;
@@ -234,7 +240,7 @@ static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
         if (IS_ERR(ld))
                 return 0;
         seq_printf(m, "%-10s %2d\n", ld->ops->name ? ld->ops->name : "???", i);
-        tty_ldisc_put(ld);
+        put_ldisc(ld);
         return 0;
 }
 
@@ -288,20 +294,17 @@ static void tty_ldisc_assign(struct tty_struct *tty, struct tty_ldisc *ld)
  *      Locking: takes tty_ldisc_lock
  */
 
-static int tty_ldisc_try(struct tty_struct *tty)
+static struct tty_ldisc *tty_ldisc_try(struct tty_struct *tty)
 {
         unsigned long flags;
         struct tty_ldisc *ld;
-        int ret = 0;
 
         spin_lock_irqsave(&tty_ldisc_lock, flags);
-        ld = tty->ldisc;
-        if (test_bit(TTY_LDISC, &tty->flags)) {
-                ld->refcount++;
-                ret = 1;
-        }
+        ld = NULL;
+        if (test_bit(TTY_LDISC, &tty->flags))
+                ld = get_ldisc(tty->ldisc);
         spin_unlock_irqrestore(&tty_ldisc_lock, flags);
-        return ret;
+        return ld;
 }
 
 /**
@@ -322,10 +325,11 @@ static int tty_ldisc_try(struct tty_struct *tty)
 
 struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
 {
+        struct tty_ldisc *ld;
+
         /* wait_event is a macro */
-        wait_event(tty_ldisc_wait, tty_ldisc_try(tty));
-        WARN_ON(tty->ldisc->refcount == 0);
-        return tty->ldisc;
+        wait_event(tty_ldisc_wait, (ld = tty_ldisc_try(tty)) != NULL);
+        return ld;
 }
 EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
 
@@ -342,9 +346,7 @@ EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
 
 struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
 {
-        if (tty_ldisc_try(tty))
-                return tty->ldisc;
-        return NULL;
+        return tty_ldisc_try(tty);
 }
 EXPORT_SYMBOL_GPL(tty_ldisc_ref);
 
@@ -360,21 +362,15 @@ EXPORT_SYMBOL_GPL(tty_ldisc_ref);
 
 void tty_ldisc_deref(struct tty_ldisc *ld)
 {
-        unsigned long flags;
-
-        BUG_ON(ld == NULL);
-
-        spin_lock_irqsave(&tty_ldisc_lock, flags);
-        if (ld->refcount == 0)
-                printk(KERN_ERR "tty_ldisc_deref: no references.\n");
-        else
-                ld->refcount--;
-        if (ld->refcount == 0)
-                wake_up(&tty_ldisc_wait);
-        spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+        put_ldisc(ld);
 }
 EXPORT_SYMBOL_GPL(tty_ldisc_deref);
 
+static inline void tty_ldisc_put(struct tty_ldisc *ld)
+{
+        put_ldisc(ld);
+}
+
 /**
  *      tty_ldisc_enable        -       allow ldisc use
  *      @tty: terminal to activate ldisc on
@@ -523,31 +519,6 @@ static int tty_ldisc_halt(struct tty_struct *tty)
 }
 
 /**
- *      tty_ldisc_wait_idle     -       wait for the ldisc to become idle
- *      @tty: tty to wait for
- *
- *      Wait for the line discipline to become idle. The discipline must
- *      have been halted for this to guarantee it remains idle.
- *
- *      tty_ldisc_lock protects the ref counts currently.
- */
-
-static int tty_ldisc_wait_idle(struct tty_struct *tty)
-{
-        unsigned long flags;
-        spin_lock_irqsave(&tty_ldisc_lock, flags);
-        while (tty->ldisc->refcount) {
-                spin_unlock_irqrestore(&tty_ldisc_lock, flags);
-                if (wait_event_timeout(tty_ldisc_wait,
-                                tty->ldisc->refcount == 0, 5 * HZ) == 0)
-                        return -EBUSY;
-                spin_lock_irqsave(&tty_ldisc_lock, flags);
-        }
-        spin_unlock_irqrestore(&tty_ldisc_lock, flags);
-        return 0;
-}
-
-/**
  *      tty_set_ldisc           -       set line discipline
  *      @tty: the terminal to set
  *      @ldisc: the line discipline
@@ -642,14 +613,6 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 
         flush_scheduled_work();
 
-        /* Let any existing reference holders finish */
-        retval = tty_ldisc_wait_idle(tty);
-        if (retval < 0) {
-                clear_bit(TTY_LDISC_CHANGING, &tty->flags);
-                tty_ldisc_put(new_ldisc);
-                return retval;
-        }
-
         mutex_lock(&tty->ldisc_mutex);
         if (test_bit(TTY_HUPPED, &tty->flags)) {
                 /* We were raced by the hangup method. It will have stomped
@@ -795,7 +758,6 @@ void tty_ldisc_hangup(struct tty_struct *tty)
                 if (tty->ldisc) {       /* Not yet closed */
                         /* Switch back to N_TTY */
                         tty_ldisc_halt(tty);
-                        tty_ldisc_wait_idle(tty);
                         tty_ldisc_reinit(tty);
                         /* At this point we have a closed ldisc and we want to
                            reopen it. We could defer this to the next open but
@@ -860,14 +822,6 @@ void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
         tty_ldisc_halt(tty);
         flush_scheduled_work();
 
-        /*
-         * Wait for any short term users (we know they are just driver
-         * side waiters as the file is closing so user count on the file
-         * side is zero.
-         */
-
-        tty_ldisc_wait_idle(tty);
-
         mutex_lock(&tty->ldisc_mutex);
         /*
          * Now kill off the ldisc
diff --git a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h
index 40f38d896777..0c4ee9b88f85 100644
--- a/include/linux/tty_ldisc.h
+++ b/include/linux/tty_ldisc.h
@@ -144,7 +144,7 @@ struct tty_ldisc_ops {
 
 struct tty_ldisc {
         struct tty_ldisc_ops *ops;
-        int refcount;
+        atomic_t users;
 };
 
 #define TTY_LDISC_MAGIC 0x5403