spinlock.h

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/* SPDX-License-Identifier: GPL-2.0-only */
 
#ifndef ARCH_SMP_SPINLOCK_H
#define ARCH_SMP_SPINLOCK_H
 
#include <thread.h>
 
/*
 * Your basic SMP spinlocks, allowing only a single CPU anywhere
 */
 
typedef struct {
        volatile unsigned int lock;
} spinlock_t;
 
#define SPIN_LOCK_UNLOCKED { 1 }
 
#define DECLARE_SPIN_LOCK(x)    \
        static spinlock_t x = SPIN_LOCK_UNLOCKED;
 
/*
 * Simple spin lock operations.  There are two variants, one clears IRQ's
 * on the local processor, one does not.
 *
 * We make no fairness assumptions. They have a cost.
 */
#define barrier() __asm__ __volatile__("" : : : "memory")
#define spin_is_locked(x)       (*(volatile int *)(&(x)->lock) <= 0)
#define spin_unlock_wait(x)     do { barrier(); } while (spin_is_locked(x))
#undef barrier
 
#define spin_lock_string \
        "\n1:\t" \
        "lock ; decl %0\n\t" \
        "js 2f\n" \
        ".section .text.lock,\"ax\"\n" \
        "2:\t" \
        "cmpl $0,%0\n\t" \
        "rep;nop\n\t" \
        "jle 2b\n\t" \
        "jmp 1b\n" \
        ".previous"
 
/*
 * This works. Despite all the confusion.
 */
#define spin_unlock_string \
        "movl $1,%0"
 
static __always_inline void spin_lock(spinlock_t *lock)
{
        __asm__ __volatile__(
                spin_lock_string
                : "=m" (lock->lock) : : "memory");
 
        /* Switching contexts while holding a spinlock will lead to deadlocks */
        thread_coop_disable();
 
}
 
static __always_inline void spin_unlock(spinlock_t *lock)
{
        thread_coop_enable();
 
        __asm__ __volatile__(
                spin_unlock_string
                : "=m" (lock->lock) : : "memory");
}
 
#endif /* ARCH_SMP_SPINLOCK_H */