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标题: USB中这段代码会不会有原子操作问题？ [打印本页]

作者: newbieforever 时间: 2011-11-15 15:32
标题: USB中这段代码会不会有原子操作问题？
/*
* Process events in the schedule, but only in one thread at a time
*/
static void uhci_scan_schedule(struct uhci_hcd *uhci)
{
int i;
struct uhci_qh *qh;

/* Don't allow re-entrant calls */
if (uhci->scan_in_progress) {
uhci->need_rescan = 1;
return;
}
uhci->scan_in_progress = 1;
rescan:
uhci->need_rescan = 0;
uhci->fsbr_is_wanted = 0;

uhci_clear_next_interrupt(uhci);
uhci_get_current_frame_number(uhci);
uhci->cur_iso_frame = uhci->frame_number;

/* Go through all the QH queues and process the URBs in each one */
for (i = 0; i < UHCI_NUM_SKELQH - 1; ++i) {
uhci->next_qh = list_entry(uhci->skelqh[i]->node.next,
struct uhci_qh, node);
while ((qh = uhci->next_qh) != uhci->skelqh[i]) {
uhci->next_qh = list_entry(qh->node.next,
struct uhci_qh, node);

if (uhci_advance_check(uhci, qh)) {
uhci_scan_qh(uhci, qh);
if (qh->state == QH_STATE_ACTIVE) {
uhci_urbp_wants_fsbr(uhci,
list_entry(qh->queue.next, struct urb_priv, node));
}
}
}
}

uhci->last_iso_frame = uhci->cur_iso_frame;
if (uhci->need_rescan)
goto rescan;
uhci->scan_in_progress = 0;

if (uhci->fsbr_is_on && !uhci->fsbr_is_wanted &&
!uhci->fsbr_expiring) {
uhci->fsbr_expiring = 1;
mod_timer(&uhci->fsbr_timer, jiffies + FSBR_OFF_DELAY);
}

if (list_empty(&uhci->skel_unlink_qh->node))
uhci_clear_next_interrupt(uhci);
else
uhci_set_next_interrupt(uhci);
}

Process events in the schedule, but only in one thread at a time，这句话说这函数一次只能在一个线程中运行，是由下面这段代码实现的：
/* Don't allow re-entrant calls */
if (uhci->scan_in_progress) {
uhci->need_rescan = 1;
return;
}
uhci->scan_in_progress = 1;

unsigned int scan_in_progress:1; /* Schedule scan is running */ 在结构体里是这样定义的，问题是不需要考虑原子操作问题吗？多个线程同时调用这个函数的时候如何保证 if (uhci->scan_in_progress) 是原子的？

作者: newbieforever 时间: 2011-11-19 12:58
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