From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934576Ab0HEWgv (ORCPT ); Thu, 5 Aug 2010 18:36:51 -0400 Received: from kroah.org ([198.145.64.141]:37688 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760856Ab0HEWYZ (ORCPT ); Thu, 5 Aug 2010 18:24:25 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Arnd Bergmann , Alan Cox , Greg Kroah-Hartman Subject: [PATCH 43/67] tty: implement BTM as mutex instead of BKL Date: Thu, 5 Aug 2010 15:23:10 -0700 Message-Id: <1281047014-23429-43-git-send-email-gregkh@suse.de> X-Mailer: git-send-email 1.7.2 In-Reply-To: <20100805213528.GA13794@kroah.com> References: <20100805213528.GA13794@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Arnd Bergmann The tty locking now follows the rules for mutexes, so we can replace the BKL usage with a new subsystem wide mutex. This patch for now makes the new behaviour an optional experimental feature that can be enabled for testing purposes. Using a regular mutex here will change the behaviour when blocked on the BTM from spinning to sleeping, but that should not be visible to the user. Using the mutex also means that all the BTM is now covered by lockdep. Signed-off-by: Arnd Bergmann Cc: Alan Cox Signed-off-by: Greg Kroah-Hartman --- drivers/char/Makefile | 1 + drivers/char/tty_mutex.c | 47 ++++++++++++++++++++++++++++++++++++++++++++++ include/linux/tty.h | 8 +++++++ lib/Kconfig.debug | 10 +++++++++ 4 files changed, 66 insertions(+), 0 deletions(-) create mode 100644 drivers/char/tty_mutex.c diff --git a/drivers/char/Makefile b/drivers/char/Makefile index 88d6eac..658bfbe 100644 --- a/drivers/char/Makefile +++ b/drivers/char/Makefile @@ -9,6 +9,7 @@ FONTMAPFILE = cp437.uni obj-y += mem.o random.o tty_io.o n_tty.o tty_ioctl.o tty_ldisc.o tty_buffer.o tty_port.o +obj-$(CONFIG_TTY_MUTEX) += tty_mutex.o obj-$(CONFIG_LEGACY_PTYS) += pty.o obj-$(CONFIG_UNIX98_PTYS) += pty.o obj-y += misc.o diff --git a/drivers/char/tty_mutex.c b/drivers/char/tty_mutex.c new file mode 100644 index 0000000..1336975 --- /dev/null +++ b/drivers/char/tty_mutex.c @@ -0,0 +1,47 @@ +/* + * drivers/char/tty_lock.c + */ +#include +#include +#include +#include +#include + +/* + * The 'big tty mutex' + * + * This mutex is taken and released by tty_lock() and tty_unlock(), + * replacing the older big kernel lock. + * It can no longer be taken recursively, and does not get + * released implicitly while sleeping. + * + * Don't use in new code. + */ +static DEFINE_MUTEX(big_tty_mutex); +struct task_struct *__big_tty_mutex_owner; +EXPORT_SYMBOL_GPL(__big_tty_mutex_owner); + +/* + * Getting the big tty mutex. + */ +void __lockfunc tty_lock(void) +{ + struct task_struct *task = current; + + WARN_ON(__big_tty_mutex_owner == task); + + mutex_lock(&big_tty_mutex); + __big_tty_mutex_owner = task; +} +EXPORT_SYMBOL(tty_lock); + +void __lockfunc tty_unlock(void) +{ + struct task_struct *task = current; + + WARN_ON(__big_tty_mutex_owner != task); + __big_tty_mutex_owner = NULL; + + mutex_unlock(&big_tty_mutex); +} +EXPORT_SYMBOL(tty_unlock); diff --git a/include/linux/tty.h b/include/linux/tty.h index 98c90df..c5e847f 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -575,7 +575,14 @@ extern int vt_ioctl(struct tty_struct *tty, struct file *file, extern long vt_compat_ioctl(struct tty_struct *tty, struct file * file, unsigned int cmd, unsigned long arg); +/* tty_mutex.c */ /* functions for preparation of BKL removal */ +#ifdef CONFIG_TTY_MUTEX +extern void __lockfunc tty_lock(void) __acquires(tty_lock); +extern void __lockfunc tty_unlock(void) __releases(tty_lock); +extern struct task_struct *__big_tty_mutex_owner; +#define tty_locked() (current == __big_tty_mutex_owner) +#else static inline void tty_lock(void) __acquires(kernel_lock) { #ifdef CONFIG_LOCK_KERNEL @@ -589,6 +596,7 @@ static inline void tty_unlock(void) __releases(kernel_lock) unlock_kernel(); } #define tty_locked() (kernel_locked()) +#endif /* * wait_event_interruptible_tty -- wait for a condition with the tty lock held diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 154ff43..2fa0979 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -428,6 +428,16 @@ config RT_MUTEX_TESTER help This option enables a rt-mutex tester. +config TTY_MUTEX + bool "Use a mutex instead of BKL for TTY locking" + depends on EXPERIMENTAL && SMP + help + The TTY subsystem traditionally depends on the big kernel lock + for serialization. Saying Y here replaces the BKL with the Big + TTY Mutex (BTM). + Building a kernel without the BKL is only possible with TTY_MUTEX + enabled. + config DEBUG_SPINLOCK bool "Spinlock and rw-lock debugging: basic checks" depends on DEBUG_KERNEL -- 1.7.2