在 2019-05-30 07:11, Eduardo Valentin 写道:
this code goes access and modify data here, e.g. msg->len and msg->buf.
On this case (I2C_SLAVE_WRITE_RECEIVED), this code wont protect access.
This can cause concurrence issues if you receive an IRQ when the user
is on your bin_read().
User will not touch 'msg = mq->curr;', just touch 'msg =
&mq->queue[mq->out];'
What happens if mq->curr == mq->queue[mq->out]?
1. The Read will check.
+ spin_lock_irqsave(&mq->lock, flags);
+ if (mq->out != mq->in) {
+ msg = &mq->queue[mq->out];
2. Flush the oldeast message. ^_^
+ case I2C_SLAVE_STOP:
+ if (unlikely(mq->truncated || msg->len < 2))
+ break;
+
+ spin_lock(&mq->lock);
+ mq->in = MQ_QUEUE_NEXT(mq->in);
+ mq->curr = &mq->queue[mq->in];
+ mq->curr->len = 0;
+
+ /* Flush the oldest message */
+ if (mq->out == mq->in)
+ mq->out = MQ_QUEUE_NEXT(mq->out);
+ spin_unlock(&mq->lock);
