tty-ldisc: make refcount be atomic_t 'users' count

This is pure preparation of changing the ldisc reference counting to be
a true refcount that defines the lifetime of the ldisc.  But this is a
purely syntactic change for now to make the next steps easier.

This patch should make no semantic changes at all. But I wanted to make
the ldisc refcount be an atomic (I will be touching it without locks
soon enough), and I wanted to rename it so that there isn't quite as
much confusion between 'ldo->refcount' (ldisk operations refcount) and
'ld->refcount' (ldisc refcount itself) in the same file.

So it's now an atomic 'ld->users' count. It still starts at zero,
despite having a reference from 'tty->ldisc', but that will change once
we turn it into a _real_ refcount.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Tested-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Tested-by: Sergey Senozhatsky <sergey.senozhatsky@mail.by>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 8 insertions, 10 deletions

diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c
index acd76b767d4c..fd175e60aad5 100644
--- a/drivers/char/tty_ldisc.c
+++ b/drivers/char/tty_ldisc.c
@@ -142,7 +142,7 @@ static struct tty_ldisc *tty_ldisc_try_get(int disc)
                         /* lock it */
                         ldops->refcount++;
                         ld->ops = ldops;
-                        ld->refcount = 0;
+                        atomic_set(&ld->users, 0);
                         err = 0;
                 }
         }
@@ -206,7 +206,7 @@ static void tty_ldisc_put(struct tty_ldisc *ld)
         ldo->refcount--;
         module_put(ldo->owner);
         spin_unlock_irqrestore(&tty_ldisc_lock, flags);
-        WARN_ON(ld->refcount);
+        WARN_ON(atomic_read(&ld->users));
         kfree(ld);
 }
 
@@ -297,7 +297,7 @@ static int tty_ldisc_try(struct tty_struct *tty)
         spin_lock_irqsave(&tty_ldisc_lock, flags);
         ld = tty->ldisc;
         if (test_bit(TTY_LDISC, &tty->flags)) {
-                ld->refcount++;
+                atomic_inc(&ld->users);
                 ret = 1;
         }
         spin_unlock_irqrestore(&tty_ldisc_lock, flags);
@@ -324,7 +324,7 @@ struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
 {
         /* wait_event is a macro */
         wait_event(tty_ldisc_wait, tty_ldisc_try(tty));
-        WARN_ON(tty->ldisc->refcount == 0);
+        WARN_ON(atomic_read(&tty->ldisc->users) == 0);
         return tty->ldisc;
 }
 EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
@@ -365,11 +365,9 @@ void tty_ldisc_deref(struct tty_ldisc *ld)
         BUG_ON(ld == NULL);
 
         spin_lock_irqsave(&tty_ldisc_lock, flags);
-        if (ld->refcount == 0)
+        if (atomic_read(&ld->users) == 0)
                 printk(KERN_ERR "tty_ldisc_deref: no references.\n");
-        else
-                ld->refcount--;
-        if (ld->refcount == 0)
+        else if (atomic_dec_and_test(&ld->users))
                 wake_up(&tty_ldisc_wait);
         spin_unlock_irqrestore(&tty_ldisc_lock, flags);
 }
@@ -536,10 +534,10 @@ static int tty_ldisc_wait_idle(struct tty_struct *tty)
 {
         unsigned long flags;
         spin_lock_irqsave(&tty_ldisc_lock, flags);
-        while (tty->ldisc->refcount) {
+        while (atomic_read(&tty->ldisc->users)) {
                 spin_unlock_irqrestore(&tty_ldisc_lock, flags);
                 if (wait_event_timeout(tty_ldisc_wait,
-                                tty->ldisc->refcount == 0, 5 * HZ) == 0)
+                                atomic_read(&tty->ldisc->users) == 0, 5 * HZ) == 0)
                         return -EBUSY;
                 spin_lock_irqsave(&tty_ldisc_lock, flags);
         }