分析rwlock的结构

分析rwlock的结构

typedef struct { volatile unsigned int lock; } rwlock_t; rwlock_t tasklist_lock __attribute__((__aligned__((1 << ((5)) )),__section__(".data.cacheline_aligned"))) = (rwlock_t) { 0x01000000 } ; ;0x01000000(RW_LOCK_UNLOCKED)是偏置值 read_lock(&tasklist_lock); 编绎为 lock ; subl $1,tasklist_lock 减1 js 2f 如果为负值表示已被write_lock锁定 1: .section .text.lock,"ax" 2: pushl % eax leal tasklist_lock,% eax 取tasklist_lock的地址 call __read_lock_failed popl % eax jmp 1b 抓锁成功了 .previous ;semaphore.c __read_lock_failed: lock ; incl (% eax) 恢复tasklist_lock的值 1: cmpl $1,(% eax) js 1b 如果tasklist_lock小于1表示write_unlock尚未解锁 lock ; decl (% eax) 准备再次抓取tasklist_lock js __read_lock_failed 它又被某个write_lock锁住了,再次循环 ret read_unlock(&tasklist_lock); 编绎为 lock ; incl tasklist_lock write_lock_irq(&tasklist_lock); 编绎为 cli lock ; subl $0x01000000,(tasklist_lock) 减去tasklist_lock的偏置值 jnz 2f 如果非0则说明它被read_lock()或write_lock()锁住了 1: .section .text.lock,"ax" 2: pushl % eax leal tasklist_lock,% eax call __write_lock_failed popl % eax jmp 1b .previous ; semaphore.c __write_lock_failed: lock ; addl $0x01000000,(% eax) 恢复tasklist_lock值 1: cmpl $0x01000000,(% eax) jne 1b 等待解锁 lock ; subl $0x01000000,(% eax) 再次抓锁 jnz __write_lock_failed 如果又被锁住的话再次循环 ret write_unlock_irq(&tasklist_lock); 编绎为: lock ; addl $0x01000000,tasklist_lock 恢复偏置值 sti