linux内核情景分析之锁机制

/*
 * These are the generic versions of the spinlocks and read-write
 * locks..
 *///自旋锁加锁,irqsave表示把标志寄存器存储起来
#define spin_lock_irqsave(lock, flags)		do { local_irq_save(flags);//关闭本地中断,保存标志位       spin_lock(lock); } while (0)
#define spin_lock_irq(lock)			do { local_irq_disable();         spin_lock(lock); } while (0)
#define spin_lock_bh(lock)			do { local_bh_disable();          spin_lock(lock); } while (0)
//读锁与下面写锁,构成读写锁
#define read_lock_irqsave(lock, flags)		do { local_irq_save(flags);       read_lock(lock); } while (0)
#define read_lock_irq(lock)			do { local_irq_disable();         read_lock(lock); } while (0)
#define read_lock_bh(lock)			do { local_bh_disable();          read_lock(lock); } while (0)
//写锁,与上面构成读写锁
#define write_lock_irqsave(lock, flags)		do { local_irq_save(flags);      write_lock(lock); } while (0)
#define write_lock_irq(lock)			do { local_irq_disable();        write_lock(lock); } while (0)
#define write_lock_bh(lock)			do { local_bh_disable();         write_lock(lock); } while (0)
//自旋锁解锁
#define spin_unlock_irqrestore(lock, flags)	do { spin_unlock(lock);  local_irq_restore(flags); } while (0)
#define spin_unlock_irq(lock)			do { spin_unlock(lock);  local_irq_enable();       } while (0)
#define spin_unlock_bh(lock)			do { spin_unlock(lock);  local_bh_enable();        } while (0)
//读锁解锁
#define read_unlock_irqrestore(lock, flags)	do { read_unlock(lock);  local_irq_restore(flags); } while (0)
#define read_unlock_irq(lock)			do { read_unlock(lock);  local_irq_enable();       } while (0)
#define read_unlock_bh(lock)			do { read_unlock(lock);  local_bh_enable();        } while (0)
//写锁解锁
#define write_unlock_irqrestore(lock, flags)	do { write_unlock(lock); local_irq_restore(flags); } while (0)
#define write_unlock_irq(lock)			do { write_unlock(lock); local_irq_enable();       } while (0)
#define write_unlock_bh(lock)			do { write_unlock(lock); local_bh_enable();        } while (0)

自旋锁加锁解析

static inline void spin_lock(spinlock_t *lock)
{
#if SPINLOCK_DEBUG
	__label__ here;
here:
	if (lock->magic != SPINLOCK_MAGIC) {//判断是否等于魔数
printk("eip: %p\n", &&here);
		BUG();
	}
#endif
	__asm__ __volatile__(
		spin_lock_string
		:"=m" (lock->lock) : : "memory");
}

其中spin_lock_string为一个宏

#define spin_lock_string \
	"\n1:\t" \
	"lock ; decb %0\n\t" \ //将lock->lock减1,指令带lock表示把总线锁住,禁止其他cpu访问
	"js 2f\n" \//不是非负数,直接进入临界区
	".section .text.lock,\"ax\"\n" \
	"2:\t" \
	"cmpb $0,%0\n\t" \//如果-1结果为负数,那就循环检测
	"rep;nop\n\t" \
	"jle 2b\n\t" \//如果检测依旧是负数,跳转到2
	"jmp 1b\n" \//否则检测
	".previous"

互斥锁,读写锁,条件变量,自旋锁(用于线程互斥)

信号量,文件锁用于进程同步

来自为知笔记(Wiz)