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))

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.

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