load-link与store-conditional (LL/SC)是一对用于并发同步访问内存的CPU指令。Load-link返回内存位置处的当前值，随后的store-conditional在该内存位置处保存新值（如果从load-link后没有被修改）。这被用于实现无锁算法与read-modify-write原子操作。

linux在<asm/atomic.h>、<asm/system.h>、<asm/cmpxchg.h>、<asm/bitops.h>、<asm/local.h>中实现了多种基本的原子操作，以最简单的atomic_add来举例：

/** atomic_add - add integer to atomic variable* @i: integer value to add* @v: pointer of type atomic_t** Atomically adds @i to @v.*/
static __inline__ void atomic_add(int i, atomic_t * v)
{if (kernel_uses_llsc && R10000_LLSC_WAR) {int temp;__asm__ __volatile__("   .set    mips3                   \n""1: ll  %0, %1      # atomic_add        \n""   addu    %0, %2                  \n""   sc  %0, %1                  \n""   beqzl   %0, 1b                  \n""   .set    mips0                   \n": "=&r" (temp), "=m" (v->counter): "Ir" (i), "m" (v->counter));} else if (kernel_uses_llsc) {int temp;__asm__ __volatile__("   .set    mips3                   \n""1: ll  %0, %1      # atomic_add        \n""   addu    %0, %2                  \n""   sc  %0, %1                  \n""   beqz    %0, 2f                  \n""   .subsection 2                   \n""2: b   1b                  \n""   .previous                   \n""   .set    mips0                   \n": "=&r" (temp), "=m" (v->counter): "Ir" (i), "m" (v->counter));} else {unsigned long flags;raw_local_irq_save(flags);v->counter += i;raw_local_irq_restore(flags);}
}

其中，kernel_uses_llsc是一个宏定义，当定义为0时就需要软件实现。raw_local_irq_save与raw_local_irq_restore函数定义在<linux/irqflags.h>，对于不同的mips cpu有不同的实现，最简单的实现如下：

    .macro irq_enable_hazard; _ssnop; _ssnop; _ssnop;; .endm.macro irq_disable_hazard; nop; nop; nop; .endm.macro  raw_local_irq_save result           .set    push                        .set    reorder                     .set    noat                        mfc0    \result, $12                    ori $1, \result, 0x1f               xori    $1, 0x1f                    .set    noreorder                   mtc0    $1, $12                     irq_disable_hazard                  .set    pop                     .endm                           .macro  raw_local_irq_restore flags         .set    push                        .set    noreorder                   .set    noat                        mfc0    $1, $12                     andi    \flags, 1                   ori $1, 0x1f                    xori    $1, 0x1f                    or  \flags, $1                  mtc0    \flags, $12                 irq_disable_hazard                  .set    pop                     .endm                           

raw_local_irq_save与raw_local_irq_restore被实现为两个mips的宏定义，raw_local_irq_save对cp0的status寄存器进行修改，让cpu进入kernek mode，ERL与EXL置0，同时禁止中断，从而保证了原子性。raw_local_irq_restore将中断使能打开。