[PATCH] mutex subsystem, core

/*

 * Mutexes: blocking mutual exclusion locks

 *

 * started by Ingo Molnar:

 *

 *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>

 *

 * This file contains the main data structure and API definitions.

 */

#ifndef __LINUX_MUTEX_H

#define __LINUX_MUTEX_H

#include <linux/list.h>

#include <linux/spinlock_types.h>

#include <asm/atomic.h>

/*

 * Simple, straightforward mutexes with strict semantics:

 *

 * - only one task can hold the mutex at a time

 * - only the owner can unlock the mutex

 * - multiple unlocks are not permitted

 * - recursive locking is not permitted

 * - a mutex object must be initialized via the API

 * - a mutex object must not be initialized via memset or copying

 * - task may not exit with mutex held

 * - memory areas where held locks reside must not be freed

 * - held mutexes must not be reinitialized

 * - mutexes may not be used in irq contexts

 *

 * These semantics are fully enforced when DEBUG_MUTEXES is

 * enabled. Furthermore, besides enforcing the above rules, the mutex

 * debugging code also implements a number of additional features

 * that make lock debugging easier and faster:

 *

 * - uses symbolic names of mutexes, whenever they are printed in debug output

 * - point-of-acquire tracking, symbolic lookup of function names

 * - list of all locks held in the system, printout of them

 * - owner tracking

 * - detects self-recursing locks and prints out all relevant info

 * - detects multi-task circular deadlocks and prints out all affected

 *   locks and tasks (and only those tasks)

 */

struct mutex {

	/* 1: unlocked, 0: locked, negative: locked, possible waiters */

	atomic_t		count;

	spinlock_t		wait_lock;

	struct list_head	wait_list;

#ifdef CONFIG_DEBUG_MUTEXES

	struct thread_info	*owner;

	struct list_head	held_list;

	unsigned long		acquire_ip;

	const char 		*name;

	void			*magic;

#endif

};

/*

 * This is the control structure for tasks blocked on mutex,

 * which resides on the blocked task's kernel stack:

 */

struct mutex_waiter {

	struct list_head	list;

	struct task_struct	*task;

#ifdef CONFIG_DEBUG_MUTEXES

	struct mutex		*lock;

	void			*magic;

#endif

};

#ifdef CONFIG_DEBUG_MUTEXES

# include <linux/mutex-debug.h>

#else

# define __DEBUG_MUTEX_INITIALIZER(lockname)

# define mutex_init(mutex)			__mutex_init(mutex, NULL)

# define mutex_destroy(mutex)				do { } while (0)

# define mutex_debug_show_all_locks()			do { } while (0)

# define mutex_debug_show_held_locks(p)			do { } while (0)

# define mutex_debug_check_no_locks_held(task)		do { } while (0)

# define mutex_debug_check_no_locks_freed(from, to)	do { } while (0)

#endif

#define __MUTEX_INITIALIZER(lockname) \

		{ .count = ATOMIC_INIT(1) \

		, .wait_lock = SPIN_LOCK_UNLOCKED \

		, .wait_list = LIST_HEAD_INIT(lockname.wait_list) \

		__DEBUG_MUTEX_INITIALIZER(lockname) }

#define DEFINE_MUTEX(mutexname) \

	struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)

extern void fastcall __mutex_init(struct mutex *lock, const char *name);

/***

 * mutex_is_locked - is the mutex locked

 * @lock: the mutex to be queried

 *

 * Returns 1 if the mutex is locked, 0 if unlocked.

 */

static inline int fastcall mutex_is_locked(struct mutex *lock)

{

	return atomic_read(&lock->count) != 1;

}

/*

 * See kernel/mutex.c for detailed documentation of these APIs.

 * Also see Documentation/mutex-design.txt.

 */

extern void fastcall mutex_lock(struct mutex *lock);

extern int fastcall mutex_lock_interruptible(struct mutex *lock);

/*

 * NOTE: mutex_trylock() follows the spin_trylock() convention,

 *       not the down_trylock() convention!

 */

extern int fastcall mutex_trylock(struct mutex *lock);

extern void fastcall mutex_unlock(struct mutex *lock);

#endif

	    sysctl.o capability.o ptrace.o timer.o user.o \

	    signal.o sys.o kmod.o workqueue.o pid.o \

	    rcupdate.o intermodule.o extable.o params.o posix-timers.o \

	    kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o

	    kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o mutex.o

obj-$(CONFIG_FUTEX) += futex.o

obj-$(CONFIG_GENERIC_ISA_DMA) += dma.o

/*

 * kernel/mutex.c

 *

 * Mutexes: blocking mutual exclusion locks

 *

 * Started by Ingo Molnar:

 *

 *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>

 *

 * Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and

 * David Howells for suggestions and improvements.

 *

 * Also see Documentation/mutex-design.txt.

 */

#include <linux/mutex.h>

#include <linux/sched.h>

#include <linux/module.h>

#include <linux/spinlock.h>

#include <linux/interrupt.h>

/*

 * In the DEBUG case we are using the "NULL fastpath" for mutexes,

 * which forces all calls into the slowpath:

 */

#ifdef CONFIG_DEBUG_MUTEXES

# include "mutex-debug.h"

# include <asm-generic/mutex-null.h>

#else

# include "mutex.h"

# include <asm/mutex.h>

#endif

/***

 * mutex_init - initialize the mutex

 * @lock: the mutex to be initialized

 *

 * Initialize the mutex to unlocked state.

 *

 * It is not allowed to initialize an already locked mutex.

 */

void fastcall __mutex_init(struct mutex *lock, const char *name)

{

	atomic_set(&lock->count, 1);

	spin_lock_init(&lock->wait_lock);

	INIT_LIST_HEAD(&lock->wait_list);

	debug_mutex_init(lock, name);

}

EXPORT_SYMBOL(__mutex_init);

/*

 * We split the mutex lock/unlock logic into separate fastpath and

 * slowpath functions, to reduce the register pressure on the fastpath.

 * We also put the fastpath first in the kernel image, to make sure the

 * branch is predicted by the CPU as default-untaken.

 */

static void fastcall noinline __sched

__mutex_lock_slowpath(atomic_t *lock_count __IP_DECL__);

/***

 * mutex_lock - acquire the mutex

 * @lock: the mutex to be acquired

 *

 * Lock the mutex exclusively for this task. If the mutex is not

 * available right now, it will sleep until it can get it.

 *

 * The mutex must later on be released by the same task that

 * acquired it. Recursive locking is not allowed. The task

 * may not exit without first unlocking the mutex. Also, kernel

 * memory where the mutex resides mutex must not be freed with

 * the mutex still locked. The mutex must first be initialized

 * (or statically defined) before it can be locked. memset()-ing

 * the mutex to 0 is not allowed.

 *

 * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging

 *   checks that will enforce the restrictions and will also do

 *   deadlock debugging. )

 *

 * This function is similar to (but not equivalent to) down().

 */

void fastcall __sched mutex_lock(struct mutex *lock)

{

	/*

	 * The locking fastpath is the 1->0 transition from

	 * 'unlocked' into 'locked' state.

	 *

	 * NOTE: if asm/mutex.h is included, then some architectures

	 * rely on mutex_lock() having _no other code_ here but this

	 * fastpath. That allows the assembly fastpath to do

	 * tail-merging optimizations. (If you want to put testcode

	 * here, do it under #ifndef CONFIG_MUTEX_DEBUG.)

	 */

	__mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);

}

EXPORT_SYMBOL(mutex_lock);

static void fastcall noinline __sched

__mutex_unlock_slowpath(atomic_t *lock_count __IP_DECL__);

/***

 * mutex_unlock - release the mutex

 * @lock: the mutex to be released

 *

 * Unlock a mutex that has been locked by this task previously.

 *

 * This function must not be used in interrupt context. Unlocking

 * of a not locked mutex is not allowed.

 *

 * This function is similar to (but not equivalent to) up().

 */

void fastcall __sched mutex_unlock(struct mutex *lock)

{

	/*

	 * The unlocking fastpath is the 0->1 transition from 'locked'

	 * into 'unlocked' state:

	 *

	 * NOTE: no other code must be here - see mutex_lock() .

	 */

	__mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);

}

EXPORT_SYMBOL(mutex_unlock);

/*

 * Lock a mutex (possibly interruptible), slowpath:

 */

static inline int __sched

__mutex_lock_common(struct mutex *lock, long state __IP_DECL__)

{

	struct task_struct *task = current;

	struct mutex_waiter waiter;

	unsigned int old_val;

	debug_mutex_init_waiter(&waiter);

	spin_lock_mutex(&lock->wait_lock);

	debug_mutex_add_waiter(lock, &waiter, task->thread_info, ip);

	/* add waiting tasks to the end of the waitqueue (FIFO): */

	list_add_tail(&waiter.list, &lock->wait_list);

	waiter.task = task;

	for (;;) {

		/*

		 * Lets try to take the lock again - this is needed even if

		 * we get here for the first time (shortly after failing to

		 * acquire the lock), to make sure that we get a wakeup once

		 * it's unlocked. Later on, if we sleep, this is the

		 * operation that gives us the lock. We xchg it to -1, so

		 * that when we release the lock, we properly wake up the

		 * other waiters:

		 */

		old_val = atomic_xchg(&lock->count, -1);

		if (old_val == 1)

			break;

		/*

		 * got a signal? (This code gets eliminated in the

		 * TASK_UNINTERRUPTIBLE case.)

		 */

		if (unlikely(state == TASK_INTERRUPTIBLE &&

						signal_pending(task))) {

			mutex_remove_waiter(lock, &waiter, task->thread_info);

			spin_unlock_mutex(&lock->wait_lock);

			debug_mutex_free_waiter(&waiter);

			return -EINTR;

		}

		__set_task_state(task, state);

		/* didnt get the lock, go to sleep: */

		spin_unlock_mutex(&lock->wait_lock);

		schedule();

		spin_lock_mutex(&lock->wait_lock);

	}

	/* got the lock - rejoice! */

	mutex_remove_waiter(lock, &waiter, task->thread_info);

	debug_mutex_set_owner(lock, task->thread_info __IP__);

	/* set it to 0 if there are no waiters left: */

	if (likely(list_empty(&lock->wait_list)))

		atomic_set(&lock->count, 0);

	spin_unlock_mutex(&lock->wait_lock);

	debug_mutex_free_waiter(&waiter);

	DEBUG_WARN_ON(list_empty(&lock->held_list));

	DEBUG_WARN_ON(lock->owner != task->thread_info);

	return 0;

}

static void fastcall noinline __sched

__mutex_lock_slowpath(atomic_t *lock_count __IP_DECL__)

{

	struct mutex *lock = container_of(lock_count, struct mutex, count);

	__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE __IP__);

}

/*

 * Release the lock, slowpath:

 */

static fastcall noinline void

__mutex_unlock_slowpath(atomic_t *lock_count __IP_DECL__)

{

        struct mutex *lock = container_of(lock_count, struct mutex, count);

	DEBUG_WARN_ON(lock->owner != current_thread_info());

	spin_lock_mutex(&lock->wait_lock);

	/*

	 * some architectures leave the lock unlocked in the fastpath failure

	 * case, others need to leave it locked. In the later case we have to

	 * unlock it here

	 */

	if (__mutex_slowpath_needs_to_unlock())

		atomic_set(&lock->count, 1);

	debug_mutex_unlock(lock);

	if (!list_empty(&lock->wait_list)) {

		/* get the first entry from the wait-list: */

		struct mutex_waiter *waiter =

				list_entry(lock->wait_list.next,

					   struct mutex_waiter, list);

		debug_mutex_wake_waiter(lock, waiter);

		wake_up_process(waiter->task);

	}

	debug_mutex_clear_owner(lock);

	spin_unlock_mutex(&lock->wait_lock);

}

/*

 * Here come the less common (and hence less performance-critical) APIs:

 * mutex_lock_interruptible() and mutex_trylock().

 */

static int fastcall noinline __sched

__mutex_lock_interruptible_slowpath(atomic_t *lock_count __IP_DECL__);

/***

 * mutex_lock_interruptible - acquire the mutex, interruptable

 * @lock: the mutex to be acquired

 *

 * Lock the mutex like mutex_lock(), and return 0 if the mutex has

 * been acquired or sleep until the mutex becomes available. If a

 * signal arrives while waiting for the lock then this function

 * returns -EINTR.

 *

 * This function is similar to (but not equivalent to) down_interruptible().

 */

int fastcall __sched mutex_lock_interruptible(struct mutex *lock)

{

	/* NOTE: no other code must be here - see mutex_lock() */

	return __mutex_fastpath_lock_retval

			(&lock->count, __mutex_lock_interruptible_slowpath);

}

EXPORT_SYMBOL(mutex_lock_interruptible);

static int fastcall noinline __sched

__mutex_lock_interruptible_slowpath(atomic_t *lock_count __IP_DECL__)

{

	struct mutex *lock = container_of(lock_count, struct mutex, count);

	return __mutex_lock_common(lock, TASK_INTERRUPTIBLE __IP__);

}

/*

 * Spinlock based trylock, we take the spinlock and check whether we

 * can get the lock:

 */

static inline int __mutex_trylock_slowpath(atomic_t *lock_count)

{

	struct mutex *lock = container_of(lock_count, struct mutex, count);

	int prev;

	spin_lock_mutex(&lock->wait_lock);

	prev = atomic_xchg(&lock->count, -1);

	if (likely(prev == 1))

		debug_mutex_set_owner(lock, current_thread_info() __RET_IP__);

	/* Set it back to 0 if there are no waiters: */

	if (likely(list_empty(&lock->wait_list)))

		atomic_set(&lock->count, 0);

	spin_unlock_mutex(&lock->wait_lock);

	return prev == 1;

}

/***

 * mutex_trylock - try acquire the mutex, without waiting

 * @lock: the mutex to be acquired

 *

 * Try to acquire the mutex atomically. Returns 1 if the mutex

 * has been acquired successfully, and 0 on contention.

 *

 * NOTE: this function follows the spin_trylock() convention, so

 * it is negated to the down_trylock() return values! Be careful

 * about this when converting semaphore users to mutexes.

 *

 * This function must not be used in interrupt context. The

 * mutex must be released by the same task that acquired it.

 */

int fastcall mutex_trylock(struct mutex *lock)

{

	return __mutex_fastpath_trylock(&lock->count,

					__mutex_trylock_slowpath);

}

EXPORT_SYMBOL(mutex_trylock);

/*

 * Mutexes: blocking mutual exclusion locks

 *

 * started by Ingo Molnar:

 *

 *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>

 *

 * This file contains mutex debugging related internal prototypes, for the

 * !CONFIG_DEBUG_MUTEXES case. Most of them are NOPs:

 */

#define spin_lock_mutex(lock)			spin_lock(lock)

#define spin_unlock_mutex(lock)			spin_unlock(lock)

#define mutex_remove_waiter(lock, waiter, ti) \

		__list_del((waiter)->list.prev, (waiter)->list.next)

#define DEBUG_WARN_ON(c)				do { } while (0)

#define debug_mutex_set_owner(lock, new_owner)		do { } while (0)

#define debug_mutex_clear_owner(lock)			do { } while (0)

#define debug_mutex_init_waiter(waiter)			do { } while (0)

#define debug_mutex_wake_waiter(lock, waiter)		do { } while (0)

#define debug_mutex_free_waiter(waiter)			do { } while (0)

#define debug_mutex_add_waiter(lock, waiter, ti, ip)	do { } while (0)

#define debug_mutex_unlock(lock)			do { } while (0)

#define debug_mutex_init(lock, name)			do { } while (0)

/*

 * Return-address parameters/declarations. They are very useful for

 * debugging, but add overhead in the !DEBUG case - so we go the

 * trouble of using this not too elegant but zero-cost solution:

 */

#define __IP_DECL__

#define __IP__

#define __RET_IP__