From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932141Ab3CKVTg (ORCPT ); Mon, 11 Mar 2013 17:19:36 -0400 Received: from mailout01.c08.mtsvc.net ([205.186.168.189]:33556 "EHLO mailout01.c08.mtsvc.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932101Ab3CKVPj (ORCPT ); Mon, 11 Mar 2013 17:15:39 -0400 From: Peter Hurley To: Greg Kroah-Hartman , Jiri Slaby Cc: Sasha Levin , Dave Jones , Sebastian Andrzej Siewior , Shawn Guo , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, Peter Hurley , Michel Lespinasse Subject: [PATCH v5 39/44] tty: Factor ldsem writer trylock Date: Mon, 11 Mar 2013 16:44:59 -0400 Message-Id: <1363034704-28036-40-git-send-email-peter@hurleysoftware.com> X-Mailer: git-send-email 1.8.1.2 In-Reply-To: <1363034704-28036-1-git-send-email-peter@hurleysoftware.com> References: <1361390599-15195-1-git-send-email-peter@hurleysoftware.com> <1363034704-28036-1-git-send-email-peter@hurleysoftware.com> X-Authenticated-User: 125194 peter@hurleysoftware.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Prepare to simplify lock acquistion by waiting writer. Derived from Michel Lespinasse's write lock stealing work on rwsem. Cc: Michel Lespinasse Signed-off-by: Peter Hurley --- drivers/tty/tty_ldsem.c | 22 +++++++++++++++------- 1 file changed, 15 insertions(+), 7 deletions(-) diff --git a/drivers/tty/tty_ldsem.c b/drivers/tty/tty_ldsem.c index d2f091a..48f1ce8 100644 --- a/drivers/tty/tty_ldsem.c +++ b/drivers/tty/tty_ldsem.c @@ -136,13 +136,8 @@ static void __ldsem_wake_readers(struct ld_semaphore *sem) sem->wait_readers = 0; } -static void __ldsem_wake_writer(struct ld_semaphore *sem) +static inline int writer_trylock(struct ld_semaphore *sem) { - struct ldsem_waiter *waiter; - struct task_struct *tsk; - - waiter = list_entry(sem->write_wait.next, struct ldsem_waiter, list); - /* only wake this writer if the active part of the count can be * transitioned from 0 -> 1 */ @@ -159,9 +154,22 @@ static void __ldsem_wake_writer(struct ld_semaphore *sem) */ count = ldsem_atomic_update(-LDSEM_ACTIVE_BIAS, sem); if (count & LDSEM_ACTIVE_MASK) - return; + return 0; } while (1); + return 1; +} + +static void __ldsem_wake_writer(struct ld_semaphore *sem) +{ + struct ldsem_waiter *waiter; + struct task_struct *tsk; + + waiter = list_entry(sem->write_wait.next, struct ldsem_waiter, list); + + if (!writer_trylock(sem)) + return; + /* We must be careful not to touch 'waiter' after we set ->task = NULL. * It is an allocated on the waiter's stack and may become invalid at * any time after that point (due to a wakeup from another source). -- 1.8.1.2