diff options
Diffstat (limited to 'tty/tty-implement-btm-as-mutex-instead-of-bkl.patch')
| -rw-r--r-- | tty/tty-implement-btm-as-mutex-instead-of-bkl.patch | 139 |
1 files changed, 139 insertions, 0 deletions
diff --git a/tty/tty-implement-btm-as-mutex-instead-of-bkl.patch b/tty/tty-implement-btm-as-mutex-instead-of-bkl.patch new file mode 100644 index 00000000000000..ce84ae064e6b9a --- /dev/null +++ b/tty/tty-implement-btm-as-mutex-instead-of-bkl.patch @@ -0,0 +1,139 @@ +From arnd@arndb.de Wed Jun 16 13:46:10 2010 +From: Arnd Bergmann <arnd@arndb.de> +Date: Tue, 1 Jun 2010 22:53:09 +0200 +Subject: tty: implement BTM as mutex instead of BKL +To: Greg KH <gregkh@suse.de> +Cc: linux-kernel@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>, Alan Cox <alan@lxorguk.ukuu.org.uk>, Frederic Weisbecker <fweisbec@gmail.com>, John Kacur <jkacur@redhat.com> +Message-ID: <1275425591-8803-30-git-send-email-arnd@arndb.de> + + +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 <arnd@arndb.de> +Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> +Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> + +--- + drivers/char/Makefile | 1 + + drivers/char/tty_mutex.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++ + include/linux/tty.h | 8 ++++++++ + lib/Kconfig.debug | 10 ++++++++++ + 4 files changed, 66 insertions(+) + +--- 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 +--- /dev/null ++++ b/drivers/char/tty_mutex.c +@@ -0,0 +1,47 @@ ++/* ++ * drivers/char/tty_lock.c ++ */ ++#include <linux/tty.h> ++#include <linux/module.h> ++#include <linux/kallsyms.h> ++#include <linux/semaphore.h> ++#include <linux/sched.h> ++ ++/* ++ * 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); +--- a/include/linux/tty.h ++++ b/include/linux/tty.h +@@ -574,7 +574,14 @@ extern int vt_ioctl(struct tty_struct *t + 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 +@@ -588,6 +595,7 @@ static inline void tty_unlock(void) __re + unlock_kernel(); + } + #define tty_locked() (kernel_locked()) ++#endif + + /* + * wait_event_interruptible_tty -- wait for a condition with the tty lock held +--- 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 |