blk-mq: pair blk_mq_start_request / blk_mq_requeue_request

Make sure we have a proper pairing between starting and requeueing
requests.  Move the dma drain and REQ_END setup into blk_mq_start_request,
and make sure blk_mq_requeue_request properly undoes them, giving us
a pair of function to prepare and unprepare a request without leaving
side effects.

Together this ensures we always clean up properly after
BLK_MQ_RQ_QUEUE_BUSY returns from ->queue_rq.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 26 insertions, 23 deletions

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 0480710a8b45..1fa9dd153fde 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -377,7 +377,7 @@ void blk_mq_complete_request(struct request *rq)
 }
 EXPORT_SYMBOL(blk_mq_complete_request);
 
-static void blk_mq_start_request(struct request *rq)
+static void blk_mq_start_request(struct request *rq, bool last)
 {
         struct request_queue *q = rq->q;
 
@@ -390,6 +390,25 @@ static void blk_mq_start_request(struct request *rq)
          */
         rq->deadline = jiffies + q->rq_timeout;
         set_bit(REQ_ATOM_STARTED, &rq->atomic_flags);
+
+        if (q->dma_drain_size && blk_rq_bytes(rq)) {
+                /*
+                 * Make sure space for the drain appears.  We know we can do
+                 * this because max_hw_segments has been adjusted to be one
+                 * fewer than the device can handle.
+                 */
+                rq->nr_phys_segments++;
+        }
+
+        /*
+         * Flag the last request in the series so that drivers know when IO
+         * should be kicked off, if they don't do it on a per-request basis.
+         *
+         * Note: the flag isn't the only condition drivers should do kick off.
+         * If drive is busy, the last request might not have the bit set.
+         */
+        if (last)
+                rq->cmd_flags |= REQ_END;
 }
 
 static void blk_mq_requeue_request(struct request *rq)
@@ -398,6 +417,11 @@ static void blk_mq_requeue_request(struct request *rq)
 
         trace_block_rq_requeue(q, rq);
         clear_bit(REQ_ATOM_STARTED, &rq->atomic_flags);
+
+        rq->cmd_flags &= ~REQ_END;
+
+        if (q->dma_drain_size && blk_rq_bytes(rq))
+                rq->nr_phys_segments--;
 }
 
 struct blk_mq_timeout_data {
@@ -565,29 +589,8 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
 
                 rq = list_first_entry(&rq_list, struct request, queuelist);
                 list_del_init(&rq->queuelist);
-                blk_mq_start_request(rq);
 
-                if (q->dma_drain_size && blk_rq_bytes(rq)) {
-                        /*
-                         * make sure space for the drain appears we
-                         * know we can do this because max_hw_segments
-                         * has been adjusted to be one fewer than the
-                         * device can handle
-                         */
-                        rq->nr_phys_segments++;
-                }
-
-                /*
-                 * Last request in the series. Flag it as such, this
-                 * enables drivers to know when IO should be kicked off,
-                 * if they don't do it on a per-request basis.
-                 *
-                 * Note: the flag isn't the only condition drivers
-                 * should do kick off. If drive is busy, the last
-                 * request might not have the bit set.
-                 */
-                if (list_empty(&rq_list))
-                        rq->cmd_flags |= REQ_END;
+                blk_mq_start_request(rq, list_empty(&rq_list));
 
                 ret = q->mq_ops->queue_rq(hctx, rq);
                 switch (ret) {