[PATCH] mutex subsystem, core

mutex implementation, core files: just the basic subsystem, no users of it.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@infradead.org>

include/linux/mutex.h

+/*
+ * 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

kernel/Makefile

@@ -7,7 +7,7 @@ obj-y     = sched.o fork.o exec_domain.o panic.o printk.o profile.o \
 	    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

+/*
+ * 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);
+
+
+

kernel/mutex.h

+/*
+ * 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__
+