diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/Makefile | 2 | ||||
| -rw-r--r-- | kernel/mutex.c | 325 | ||||
| -rw-r--r-- | kernel/mutex.h | 35 |
3 files changed, 361 insertions, 1 deletions
diff --git a/kernel/Makefile b/kernel/Makefile index 4f5a1453093..de580b4d54a 100644 --- a/kernel/Makefile +++ b/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 diff --git a/kernel/mutex.c b/kernel/mutex.c new file mode 100644 index 00000000000..7eb96066144 --- /dev/null +++ b/kernel/mutex.c @@ -0,0 +1,325 @@ +/* + * 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); + + + diff --git a/kernel/mutex.h b/kernel/mutex.h new file mode 100644 index 00000000000..00fe84e7b67 --- /dev/null +++ b/kernel/mutex.h @@ -0,0 +1,35 @@ +/* + * 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__ + |