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authorIngo Molnar <mingo@elte.hu>2006-01-09 15:59:19 -0800
committerIngo Molnar <mingo@hera.kernel.org>2006-01-09 15:59:19 -0800
commit6053ee3b32e3437e8c1e72687850f436e779bd49 (patch)
treebb845004eb66554c569bc53a1efc87365c8a3cbe /kernel/mutex.c
parent2acbb8c657af86b2fa5b185f1d7048385e310585 (diff)
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[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>
Diffstat (limited to 'kernel/mutex.c')
-rw-r--r--kernel/mutex.c325
1 files changed, 325 insertions, 0 deletions
diff --git a/kernel/mutex.c b/kernel/mutex.c
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+++ b/kernel/mutex.c
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+/*
+ * 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);
+
+
+