[patch 6/8] mutex subsystem, core

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mutex implementation, core files: just the basic subsystem, no users of it.

Signed-off-by: Ingo Molnar <[email protected]>

----

 include/linux/mutex.h |  100 +++++++++++
 kernel/Makefile       |    2 
 kernel/mutex.c        |  453 ++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 554 insertions(+), 1 deletion(-)

Index: linux/include/linux/mutex.h
===================================================================
--- /dev/null
+++ linux/include/linux/mutex.h
@@ -0,0 +1,100 @@
+#ifndef __LINUX_MUTEX_H
+#define __LINUX_MUTEX_H
+
+/*
+ * Mutexes: blocking mutual exclusion locks
+ *
+ * started by Ingo Molnar:
+ *
+ *  Copyright (C) 2004, 2005 Red Hat, Inc., Ingo Molnar <[email protected]>
+ *
+ * This file contains the main data structure and API definitions.
+ */
+#include <linux/config.h>
+#include <asm/atomic.h>
+#include <linux/list.h>
+#include <linux/spinlock_types.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 mutex		*lock;
+	struct list_head	list;
+	struct thread_info	*ti;
+#ifdef CONFIG_DEBUG_MUTEXES
+	void			*magic;
+#endif
+};
+
+#ifdef CONFIG_DEBUG_MUTEXES
+# include <linux/mutex-debug.h>
+#else
+# define __DEBUG_MUTEX_INITIALIZER(lockname)
+# define mutex_init(sem)				__mutex_init(sem, NULL)
+# 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));
+
+extern void FASTCALL(mutex_lock(struct mutex *lock));
+extern int FASTCALL(mutex_lock_interruptible(struct mutex *lock));
+extern int FASTCALL(mutex_trylock(struct mutex *lock));
+extern void FASTCALL(mutex_unlock(struct mutex *lock));
+extern int FASTCALL(mutex_is_locked(struct mutex *lock));
+
+#endif
Index: linux/kernel/Makefile
===================================================================
--- linux.orig/kernel/Makefile
+++ linux/kernel/Makefile
@@ -7,7 +7,7 @@ obj-y     = sched.o fork.o exec_domain.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
Index: linux/kernel/mutex.c
===================================================================
--- /dev/null
+++ linux/kernel/mutex.c
@@ -0,0 +1,453 @@
+/*
+ * kernel/mutex.c
+ *
+ * Mutexes: blocking mutual exclusion locks
+ *
+ * Started by Ingo Molnar:
+ *
+ *  Copyright (C) 2004, 2005 Red Hat, Inc., Ingo Molnar <[email protected]>
+ *
+ * Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and
+ * David Howells for suggestions and improvements.
+ */
+#include <linux/mutex.h>
+#include <linux/sched.h>
+#include <linux/delay.h>
+#include <linux/module.h>
+#include <linux/spinlock.h>
+#include <linux/kallsyms.h>
+#include <linux/syscalls.h>
+#include <linux/interrupt.h>
+
+/*
+ * Debugging constructs - they are NOPs in the !DEBUG case:
+ */
+#ifdef CONFIG_DEBUG_MUTEXES
+# include "mutex-debug.c"
+#else
+/*
+ * We can speed up the lock-acquire and lock-release codepath, if
+ * there's no debugging state to be set up (!DEBUG_MUTEXES).
+ */
+# define MUTEX_LOCKLESS_FASTPATH
+
+/*
+ * Return-address parameters/declarations that are NOPs in the !DEBUG case:
+ */
+# define __IP_DECL__
+# define __IP__
+# define __CALLER_IP__
+
+# define spin_lock_mutex(lock)			spin_lock(lock)
+# define spin_unlock_mutex(lock)		spin_unlock(lock)
+
+# define DEBUG_WARN_ON(c)			do { } while (0)
+
+# define debug_set_owner(lock, new_owner)	do { } while (0)
+# define debug_clear_owner(lock)		do { } while (0)
+# define debug_init_waiter(waiter)		do { } while (0)
+# define debug_wake_waiter(lock, waiter)	do { } while (0)
+# define debug_free_waiter(waiter)		do { } while (0)
+# define debug_add_waiter(lock, waiter, ti, ip)	do { } while (0)
+# define debug_remove_waiter(lock, waiter, ti)	do { } while (0)
+# define debug_mutex_unlock(lock)		do { } while (0)
+# define debug_mutex_init(lock, name)		do { } while (0)
+#endif /* !CONFIG_DEBUG_MUTEXES */
+
+/*
+ * Block on a lock - add ourselves to the list of waiters.
+ * Called with lock->wait_lock held.
+ */
+static inline void
+add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
+	   struct thread_info *ti __IP_DECL__)
+{
+	debug_add_waiter(lock, waiter, ti, ip);
+
+	waiter->lock = lock;
+	waiter->ti = ti;
+
+	/* Add waiting tasks to the end of the waitqueue (FIFO): */
+	list_add_tail(&waiter->list, &lock->wait_list);
+}
+
+/*
+ * Wake up a task and make it the new owner of the mutex:
+ */
+static inline void
+mutex_wakeup_waiter(struct mutex *lock __IP_DECL__)
+{
+	struct mutex_waiter *waiter;
+
+	/* get the first entry from the wait-list: */
+	waiter = list_entry(lock->wait_list.next, struct mutex_waiter, list);
+
+	debug_wake_waiter(lock, waiter);
+
+	wake_up_process(waiter->ti->task);
+}
+
+static inline void
+remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
+	      struct thread_info *ti)
+{
+	debug_remove_waiter(lock, waiter, ti);
+
+	list_del_init(&waiter->list);
+	waiter->ti = NULL;
+}
+
+/*
+ * Lock a mutex, common slowpath. We just decremented the count,
+ * and it got negative as a result.
+ *
+ * We enter with the lock held, and return with it released.
+ */
+static inline int
+__mutex_lock_common(struct mutex *lock, struct mutex_waiter *waiter,
+		    struct thread_info *ti,
+		    unsigned long task_state __IP_DECL__)
+{
+	struct task_struct *task = ti->task;
+	unsigned int old_val;
+
+	add_waiter(lock, waiter, ti __IP__);
+	__set_task_state(task, task_state);
+
+	/*
+	 * 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 this is the operation that gives
+	 * us the lock. We need to xchg it to -1, so that when we
+	 * release the lock, we properly wake up other waiters!
+	 */
+	old_val = atomic_xchg(&lock->count, -1);
+
+	if (unlikely(old_val == 1)) {
+		/*
+		 * Got the lock! Rejoice:
+		 */
+		debug_set_owner(lock, ti __IP__);
+		remove_waiter(lock, waiter, ti);
+
+		spin_unlock_mutex(&lock->wait_lock);
+
+		debug_free_waiter(waiter);
+
+		DEBUG_WARN_ON(list_empty(&lock->held_list));
+		DEBUG_WARN_ON(lock->owner != ti);
+
+		__set_task_state(task, TASK_RUNNING);
+
+		return 1;
+	}
+
+	/*
+	 * Ok, didnt get the lock - we'll go to sleep after return:
+	 */
+	spin_unlock_mutex(&lock->wait_lock);
+
+	return 0;
+}
+
+/*
+ * Lock the mutex:
+ */
+static inline void __mutex_lock_nonatomic(struct mutex *lock __IP_DECL__)
+{
+	struct thread_info *ti = current_thread_info();
+	struct mutex_waiter waiter;
+
+	spin_lock_mutex(&lock->wait_lock);
+
+	/* releases the lock: */
+	while (!__mutex_lock_common(lock, &waiter, ti,
+					TASK_UNINTERRUPTIBLE __IP__)) {
+		/* wait to be woken up: */
+		schedule();
+
+		spin_lock_mutex(&lock->wait_lock);
+
+		remove_waiter(lock, &waiter, ti);
+	}
+}
+
+/*
+ * Lock a mutex interruptible:
+ */
+static int __sched
+__mutex_lock_interruptible_nonatomic(struct mutex *lock __IP_DECL__)
+{
+	struct thread_info *ti = current_thread_info();
+	struct mutex_waiter waiter;
+
+	spin_lock_mutex(&lock->wait_lock);
+
+	for (;;) {
+		/* releases the lock: */
+		if (__mutex_lock_common(lock, &waiter, ti,
+						TASK_INTERRUPTIBLE __IP__))
+			return 0;
+
+		/* break out on a signal: */
+		if (signal_pending(ti->task))
+			break;
+
+		/* wait to be given the lock: */
+		schedule();
+
+		spin_lock_mutex(&lock->wait_lock);
+
+		remove_waiter(lock, &waiter, ti);
+	}
+	/*
+	 * We got a signal. Remove ourselves from the wait list:
+	 */
+	remove_waiter(lock, &waiter, ti);
+	/*
+	 * If there are other waiters then wake
+	 * one up:
+	 */
+	if (!list_empty(&lock->wait_list))
+		mutex_wakeup_waiter(lock __IP__);
+
+	spin_unlock_mutex(&lock->wait_lock);
+
+	__set_task_state(ti->task, TASK_RUNNING);
+
+	debug_free_waiter(&waiter);
+
+	return -EINTR;
+}
+
+/*
+ * Mutex trylock, returns 1 if successful, 0 if contention
+ */
+#ifdef MUTEX_LOCKLESS_FASTPATH
+
+/*
+ * We have two fastpath variants. The cmpxchg based one is
+ * better (because it has no side-effect on mutex_unlock()),
+ * but cmpxchg is not available on every architecture, so we
+ * provide an atomic_dec_return based variant too:
+ */
+#ifdef __HAVE_ARCH_CMPXCHG
+static int __mutex_trylock(struct mutex *lock __IP_DECL__)
+{
+	if (atomic_cmpxchg(&lock->count, 1, 0) == 1)
+		return 1;
+	return 0;
+}
+#else
+static int __mutex_trylock(struct mutex *lock)
+{
+	/*
+	 * If we do not get the lock then we have the counter
+	 * negative, but that's not a big problem, it will
+	 * force the next mutex_unlock() into the slowpath.
+	 */
+	if (atomic_dec_return(&lock->count) < 0)
+		return 0;
+	return 1;
+}
+#endif
+
+#else /* !MUTEX_LOCKLESS_FASTPATH */
+
+static int __mutex_trylock(struct mutex *lock __IP_DECL__)
+{
+	struct thread_info *ti = current_thread_info();
+	int ret = 0;
+
+	spin_lock_mutex(&lock->wait_lock);
+
+	if (atomic_read(&lock->count) == 1) {
+		atomic_set(&lock->count, 0);
+		debug_set_owner(lock, ti __IP__);
+		ret = 1;
+	}
+
+	spin_unlock_mutex(&lock->wait_lock);
+
+	return ret;
+}
+#endif /* !MUTEX_LOCKLESS_FASTPATH */
+
+int fastcall mutex_is_locked(struct mutex *lock)
+{
+	smp_mb();
+	return atomic_read(&lock->count) != 1;
+}
+
+EXPORT_SYMBOL_GPL(mutex_is_locked);
+
+int fastcall mutex_trylock(struct mutex *lock)
+{
+	return __mutex_trylock(lock __CALLER_IP__);
+}
+
+/*
+ * Release the lock:
+ */
+static inline void __mutex_unlock_nonatomic(struct mutex *lock __IP_DECL__)
+{
+	spin_lock_mutex(&lock->wait_lock);
+
+	debug_mutex_unlock(lock);
+
+	/*
+	 * Set it back to 'unlocked'. We'll have a waiter in flight
+	 * (if any), and if some other task comes around, let it
+	 * steal the lock. Waiters take care of themselves and stay
+	 * in flight until necessary.
+	 */
+	atomic_set(&lock->count, 1);
+
+	if (!list_empty(&lock->wait_list))
+		mutex_wakeup_waiter(lock __IP__);
+
+	debug_clear_owner(lock);
+
+	spin_unlock_mutex(&lock->wait_lock);
+}
+
+#ifdef MUTEX_LOCKLESS_FASTPATH
+
+/*
+ * We split it into a fastpath and a separate slowpath function,
+ * to reduce the register pressure on the fastpath:
+ *
+ * We want the atomic op come first, to make sure the
+ * branch is predicted as default-untaken:
+ */
+static __sched void FASTCALL(__mutex_lock_noinline(atomic_t *lock_count));
+
+/*
+ * The locking fastpath is the 1->0 transition from
+ * 'unlocked' into 'locked' state:
+ */
+static inline void __mutex_lock_atomic(struct mutex *lock)
+{
+	atomic_dec_call_if_negative(&lock->count, __mutex_lock_noinline);
+}
+
+static fastcall __sched void __mutex_lock_noinline(atomic_t *lock_count)
+{
+	struct mutex *lock = container_of(lock_count, struct mutex, count);
+
+	__mutex_lock_nonatomic(lock);
+}
+
+static inline void __mutex_lock(struct mutex *lock)
+{
+	__mutex_lock_atomic(lock);
+}
+
+static inline int __mutex_lock_interruptible(struct mutex *lock)
+{
+	if (unlikely(atomic_dec_return(&lock->count) < 0))
+		return __mutex_lock_interruptible_nonatomic(lock);
+	return 0;
+}
+
+static void __sched FASTCALL(__mutex_unlock_noinline(atomic_t *lock_count));
+
+/*
+ * The unlocking fastpath is the 0->1 transition from
+ * 'locked' into 'unlocked' state:
+ */
+static inline void __mutex_unlock_atomic(struct mutex *lock)
+{
+	atomic_inc_call_if_nonpositive(&lock->count, __mutex_unlock_noinline);
+}
+
+static fastcall void __sched __mutex_unlock_noinline(atomic_t *lock_count)
+{
+	struct mutex *lock = container_of(lock_count, struct mutex, count);
+
+	__mutex_unlock_nonatomic(lock);
+}
+
+static inline void __mutex_unlock(struct mutex *lock)
+{
+	__mutex_unlock_atomic(lock);
+}
+
+#else
+
+static inline void __mutex_lock(struct mutex *lock __IP_DECL__)
+{
+	__mutex_lock_nonatomic(lock __IP__);
+}
+
+static inline void __mutex_unlock(struct mutex *lock __IP_DECL__)
+{
+	__mutex_unlock_nonatomic(lock __IP__);
+}
+
+static inline int __mutex_lock_interruptible(struct mutex *lock __IP_DECL__)
+{
+	return __mutex_lock_interruptible_nonatomic(lock __IP__);
+}
+
+#endif
+
+/*
+ * Some architectures provide hand-coded mutex_lock() functions,
+ * the will call the mutex_*_slowpath() generic functions:
+ */
+#ifdef ARCH_IMPLEMENTS_MUTEX_FASTPATH
+
+void __sched fastcall mutex_lock_slowpath(struct mutex *lock)
+{
+	__mutex_lock(lock);
+}
+
+void __sched fastcall mutex_unlock_slowpath(struct mutex *lock)
+{
+	__mutex_unlock(lock);
+}
+
+int __sched fastcall mutex_lock_interruptible_slowpath(struct mutex *lock)
+{
+	return __mutex_lock_interruptible(lock);
+}
+
+#else
+
+void __sched fastcall mutex_lock(struct mutex *lock)
+{
+	__mutex_lock(lock __CALLER_IP__);
+}
+
+void __sched fastcall mutex_unlock(struct mutex *lock)
+{
+	DEBUG_WARN_ON(lock->owner != current_thread_info());
+	__mutex_unlock(lock __CALLER_IP__);
+}
+
+int __sched fastcall mutex_lock_interruptible(struct mutex *lock)
+{
+	return __mutex_lock_interruptible(lock __CALLER_IP__);
+}
+
+#endif
+
+EXPORT_SYMBOL_GPL(mutex_lock);
+EXPORT_SYMBOL_GPL(mutex_unlock);
+EXPORT_SYMBOL_GPL(mutex_lock_interruptible);
+
+/*
+ * Initialise the lock:
+ */
+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_GPL(__mutex_init);
+
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