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>

diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c
index acd76b7..fd175e6 100644 (file)
--- 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);
        }

diff --git a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h
index 40f38d8..0c4ee9b 100644 (file)
--- 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