static void __blk_mq_requeue_request(struct request *rq)
{
struct request_queue *q = rq->q;
+ enum mq_rq_state old_state = blk_mq_rq_state(rq);
blk_mq_put_driver_tag(rq);
trace_block_rq_requeue(q, rq);
wbt_requeue(q->rq_wb, &rq->issue_stat);
- if (blk_mq_rq_state(rq) != MQ_RQ_IDLE) {
- blk_mq_rq_update_state(rq, MQ_RQ_IDLE);
+ if (old_state != MQ_RQ_IDLE) {
+ if (!blk_mq_change_rq_state(rq, old_state, MQ_RQ_IDLE))
+ WARN_ON_ONCE(true);
if (q->dma_drain_size && blk_rq_bytes(rq))
rq->nr_phys_segments--;
}
Can you explain why was old_state kept as a local variable?
Hello Sagi,
Since blk_mq_requeue_request() must be called after a request has completed
the timeout handler will ignore requests that are being requeued. Hence it
is safe in this function to cache the request state in a local variable.
I understand why it is safe, I just didn't understand why it is needed.
+static inline bool blk_mq_change_rq_state(struct request *rq,
+ enum mq_rq_state old_state,
+ enum mq_rq_state new_state)
{
- u64 old_val = READ_ONCE(rq->gstate);
- u64 new_val = (old_val & ~MQ_RQ_STATE_MASK) | state;
-
- if (state == MQ_RQ_IN_FLIGHT) {
- WARN_ON_ONCE((old_val & MQ_RQ_STATE_MASK) != MQ_RQ_IDLE);
- new_val += MQ_RQ_GEN_INC;
- }
+ unsigned long old_val = (READ_ONCE(rq->__deadline) & ~RQ_STATE_MASK) |
+ old_state;
+ unsigned long new_val = (old_val & ~RQ_STATE_MASK) | new_state;
- /* avoid exposing interim values */
- WRITE_ONCE(rq->gstate, new_val);
+ return cmpxchg(&rq->__deadline, old_val, new_val) == old_val;
}
Can you explain why this takes the old_state of the request?
Can you clarify your question? The purpose of this function is to change
the request state only into @new_state if it matches @old_state. I think
that is also what the implementation of this function does.
I misread the documentation of this. never mind. thanks.