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/*
* Copyright (c) 2018 Intel Corporation.
*
* SPDX-License-Identifier: Apache-2.0
*/
/**
* @file
* @brief Public interface for spinlocks
*/
#ifndef ZEPHYR_INCLUDE_SPINLOCK_H_
#define ZEPHYR_INCLUDE_SPINLOCK_H_
#include <sys/atomic.h>
#include <sys/__assert.h>
#include <stdbool.h>
#include <arch/cpu.h>
#ifdef __cplusplus
extern "C" {
#endif
/**
* @brief Spinlock APIs
* @defgroup spinlock_apis Spinlock APIs
* @ingroup kernel_apis
* @{
*/
struct z_spinlock_key {
int key;
};
/**
* @brief Kernel Spin Lock
*
* This struct defines a spin lock record on which CPUs can wait with
* k_spin_lock(). Any number of spinlocks may be defined in
* application code.
*/
struct k_spinlock {
#ifdef CONFIG_SMP
atomic_t locked;
#endif
#ifdef CONFIG_SPIN_VALIDATE
/* Stores the thread that holds the lock with the locking CPU
* ID in the bottom two bits.
*/
uintptr_t thread_cpu;
#endif
#if defined(CONFIG_CPLUSPLUS) && !defined(CONFIG_SMP) && \
!defined(CONFIG_SPIN_VALIDATE)
/* If CONFIG_SMP and CONFIG_SPIN_VALIDATE are both not defined
* the k_spinlock struct will have no members. The result
* is that in C sizeof(k_spinlock) is 0 and in C++ it is 1.
*
* This size difference causes problems when the k_spinlock
* is embedded into another struct like k_msgq, because C and
* C++ will have different ideas on the offsets of the members
* that come after the k_spinlock member.
*
* To prevent this we add a 1 byte dummy member to k_spinlock
* when the user selects C++ support and k_spinlock would
* otherwise be empty.
*/
char dummy;
#endif
};
/* There's a spinlock validation framework available when asserts are
* enabled. It adds a relatively hefty overhead (about 3k or so) to
* kernel code size, don't use on platforms known to be small.
*/
#ifdef CONFIG_SPIN_VALIDATE
bool z_spin_lock_valid(struct k_spinlock *l);
bool z_spin_unlock_valid(struct k_spinlock *l);
void z_spin_lock_set_owner(struct k_spinlock *l);
BUILD_ASSERT(CONFIG_MP_NUM_CPUS <= 4, "Too many CPUs for mask");
# ifdef CONFIG_KERNEL_COHERENCE
bool z_spin_lock_mem_coherent(struct k_spinlock *l);
# endif /* CONFIG_KERNEL_COHERENCE */
#endif /* CONFIG_SPIN_VALIDATE */
/**
* @brief Spinlock key type
*
* This type defines a "key" value used by a spinlock implementation
* to store the system interrupt state at the time of a call to
* k_spin_lock(). It is expected to be passed to a matching
* k_spin_unlock().
*
* This type is opaque and should not be inspected by application
* code.
*/
typedef struct z_spinlock_key k_spinlock_key_t;
/**
* @brief Lock a spinlock
*
* This routine locks the specified spinlock, returning a key handle
* representing interrupt state needed at unlock time. Upon
* returning, the calling thread is guaranteed not to be suspended or
* interrupted on its current CPU until it calls k_spin_unlock(). The
* implementation guarantees mutual exclusion: exactly one thread on
* one CPU will return from k_spin_lock() at a time. Other CPUs
* trying to acquire a lock already held by another CPU will enter an
* implementation-defined busy loop ("spinning") until the lock is
* released.
*
* Separate spin locks may be nested. It is legal to lock an
* (unlocked) spin lock while holding a different lock. Spin locks
* are not recursive, however: an attempt to acquire a spin lock that
* the CPU already holds will deadlock.
*
* In circumstances where only one CPU exists, the behavior of
* k_spin_lock() remains as specified above, though obviously no
* spinning will take place. Implementations may be free to optimize
* in uniprocessor contexts such that the locking reduces to an
* interrupt mask operation.
*
* @param l A pointer to the spinlock to lock
* @return A key value that must be passed to k_spin_unlock() when the
* lock is released.
*/
static ALWAYS_INLINE k_spinlock_key_t k_spin_lock(struct k_spinlock *l)
{
ARG_UNUSED(l);
k_spinlock_key_t k;
/* Note that we need to use the underlying arch-specific lock
* implementation. The "irq_lock()" API in SMP context is
* actually a wrapper for a global spinlock!
*/
k.key = arch_irq_lock();
#ifdef CONFIG_SPIN_VALIDATE
__ASSERT(z_spin_lock_valid(l), "Recursive spinlock %p", l);
# ifdef CONFIG_KERNEL_COHERENCE
__ASSERT_NO_MSG(z_spin_lock_mem_coherent(l));
# endif
#endif
#ifdef CONFIG_SMP
while (!atomic_cas(&l->locked, 0, 1)) {
}
#endif
#ifdef CONFIG_SPIN_VALIDATE
z_spin_lock_set_owner(l);
#endif
return k;
}
/**
* @brief Unlock a spin lock
*
* This releases a lock acquired by k_spin_lock(). After this
* function is called, any CPU will be able to acquire the lock. If
* other CPUs are currently spinning inside k_spin_lock() waiting for
* this lock, exactly one of them will return synchronously with the
* lock held.
*
* Spin locks must be properly nested. A call to k_spin_unlock() must
* be made on the lock object most recently locked using
* k_spin_lock(), using the key value that it returned. Attempts to
* unlock mis-nested locks, or to unlock locks that are not held, or
* to passing a key parameter other than the one returned from
* k_spin_lock(), are illegal. When CONFIG_SPIN_VALIDATE is set, some
* of these errors can be detected by the framework.
*
* @param l A pointer to the spinlock to release
* @param key The value returned from k_spin_lock() when this lock was
* acquired
*/
static ALWAYS_INLINE void k_spin_unlock(struct k_spinlock *l,
k_spinlock_key_t key)
{
ARG_UNUSED(l);
#ifdef CONFIG_SPIN_VALIDATE
__ASSERT(z_spin_unlock_valid(l), "Not my spinlock %p", l);
#endif
#ifdef CONFIG_SMP
/* Strictly we don't need atomic_clear() here (which is an
* exchange operation that returns the old value). We are always
* setting a zero and (because we hold the lock) know the existing
* state won't change due to a race. But some architectures need
* a memory barrier when used like this, and we don't have a
* Zephyr framework for that.
*/
atomic_clear(&l->locked);
#endif
arch_irq_unlock(key.key);
}
/* Internal function: releases the lock, but leaves local interrupts
* disabled
*/
static ALWAYS_INLINE void k_spin_release(struct k_spinlock *l)
{
ARG_UNUSED(l);
#ifdef CONFIG_SPIN_VALIDATE
__ASSERT(z_spin_unlock_valid(l), "Not my spinlock %p", l);
#endif
#ifdef CONFIG_SMP
atomic_clear(&l->locked);
#endif
}
/** @} */
#ifdef __cplusplus
}
#endif
#endif /* ZEPHYR_INCLUDE_SPINLOCK_H_ */