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tty: implement BTM as mutex instead of BKL

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The tty locking now follows the rules for mutexes, so
we can replace the BKL usage with a new subsystem
wide mutex.

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>
This commit is contained in:
Arnd Bergmann 2010-08-06 21:40:30 +02:00 committed by Greg Kroah-Hartman
parent ddcd9fb66a
commit b07471fa51
3 changed files with 53 additions and 13 deletions
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1
drivers/char/Makefile
View file

@ -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-y += tty_mutex.o
obj-$(CONFIG_LEGACY_PTYS) += pty.o
obj-$(CONFIG_UNIX98_PTYS) += pty.o
obj-y += misc.o

47
drivers/char/tty_mutex.c Normal file
View file

@ -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);

18
include/linux/tty.h
View file

@ -578,20 +578,12 @@ 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 */
static inline void tty_lock(void) __acquires(kernel_lock)
{
#ifdef CONFIG_LOCK_KERNEL
/* kernel_locked is 1 for !CONFIG_LOCK_KERNEL */
WARN_ON(kernel_locked());
#endif
lock_kernel();
}
static inline void tty_unlock(void) __releases(kernel_lock)
{
unlock_kernel();
}
#define tty_locked() (kernel_locked())
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)
/*
* wait_event_interruptible_tty -- wait for a condition with the tty lock held