make_request函数中的一个bug

 110repeat:
 111/* we don't allow the write-requests to fill up the queue completely:
 112 * we want some room for reads: they take precedence. The last third
 113 * of the requests are only for reads.
 114 */
 115        if (rw == READ)
 116                req = request+NR_REQUEST;
 117        else
 118                req = request+((NR_REQUEST*2)/3);
 119/* find an empty request */
 120        while (--req >= request)
 121                if (req->dev<0)
 122                        break;
 123/* if none found, sleep on new requests: check for rw_ahead */
 124        if (req < request) {
 125                if (rw_ahead) {
 126                        unlock_buffer(bh);
                            sti();
 127                        return;
 128                }
 129                sleep_on(&wait_for_request);
 130                goto repeat;
 131        }

该段代码取自kernel/blk_drv/ll_rw_blk.c

代码进入代码跟离开代码的时候应该本别加上cli/sti用来禁止中断。具体原因请参看另外一篇博客。(http://www.cnblogs.com/gitclubs/archive/2012/02/23/2365300.html)

因为这段代码操作的数据request数组以及wait_for_request变量，很有可能在某个中断中被修改，因此此处应该改为如下代码：

 109        cli();
 110repeat:
 111/* we don't allow the write-requests to fill up the queue completely:
 112 * we want some room for reads: they take precedence. The last third
 113 * of the requests are only for reads.
 114 */
 115        if (rw == READ)
 116                req = request+NR_REQUEST;
 117        else
 118                req = request+((NR_REQUEST*2)/3);
 119/* find an empty request */
 120        while (--req >= request)
 121                if (req->dev<0)
 122                        break;
 123/* if none found, sleep on new requests: check for rw_ahead */
 124        if (req < request) {
 125                if (rw_ahead) {
 126                        unlock_buffer(bh);
 127                        return;
 128                }
 129                sleep_on(&wait_for_request);
 130                goto repeat;
 131        }
 132        sti();