From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753218AbZHCR6t (ORCPT ); Mon, 3 Aug 2009 13:58:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752035AbZHCR6s (ORCPT ); Mon, 3 Aug 2009 13:58:48 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:59233 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751992AbZHCR6s (ORCPT ); Mon, 3 Aug 2009 13:58:48 -0400 Date: Mon, 3 Aug 2009 10:58:29 -0700 (PDT) From: Linus Torvalds X-X-Sender: torvalds@localhost.localdomain To: Alan Cox cc: OGAWA Hirofumi , Sergey Senozhatsky , Linux Kernel Mailing List , Greg KH Subject: [PATCH 1/2] tty-ldisc: make refcount be atomic_t 'users' count In-Reply-To: Message-ID: References: <20090802120120.GA3097@localdomain.by> <20090802190514.GA3278@localdomain.by> <87k51l9apo.fsf@devron.myhome.or.jp> <20090802234851.3fd1ac2c@lxorguk.ukuu.org.uk> User-Agent: Alpine 2.01 (LFD 1184 2008-12-16) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Linus Torvalds Date: Mon, 3 Aug 2009 10:07:09 -0700 Subject: [PATCH 1/2] 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. Signed-off-by: Linus Torvalds --- 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. drivers/char/tty_ldisc.c | 18 ++++++++---------- include/linux/tty_ldisc.h | 2 +- 2 files changed, 9 insertions(+), 11 deletions(-) diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c index acd76b7..fd175e6 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); } diff --git a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h index 40f38d8..0c4ee9b 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 -- 1.6.4.21.g73b866