/* * 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){ might_sleep(); /* * The locking fastpath is the 1->0 transition from * 'unlocked' into 'locked' state. */ __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: */ __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){ might_sleep(); 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.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)
{
might_sleep();
/*
* The locking fastpath is the 1->0 transition from
* 'unlocked' into 'locked' state.
*/
__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:
*/
__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)
{
might_sleep();
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);