[PATCH 1/2] blk-mq: provide way to reset rq deadline

[keith.busch@intel.com (Keith Busch)]

If hardware has temporarily paused processing requests that its driver
has dispatched, the driver may need to halt timeout detection during that
temporary stoppage. When the hardware has un-paused request processing,
the driver needs a way to rebase all dispatched request dealines using
current jiffies so that time accrued during the paused state doesn't
count against that request.

Signed-off-by: Keith Busch <keith.busch at intel.com>
---
 block/blk-mq.c         | 30 ++++++++++++++++++++++++++++++
 include/linux/blk-mq.h |  1 +
 2 files changed, 31 insertions(+)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 08a6248d8536..9d85903d4e0c 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -960,6 +960,36 @@ static void blk_mq_timeout_work(struct work_struct *work)
 	blk_queue_exit(q);
 }
 
+static bool blk_mq_reset_rq(struct blk_mq_hw_ctx *hctx, struct request *rq,
+			    void *priv, bool reserved)
+{
+	if (blk_mq_rq_state(rq) == MQ_RQ_IN_FLIGHT)
+		blk_add_timer(rq);
+	return true;
+}
+
+/**
+ * blk_mq_reset_rqs - reset the timers on all inflight requests
+ *
+ * @q - request queue to iterate
+ *
+ * This is intended for use when a driver detects its hardware has temporarily
+ * paused processing commands. When the condition is initially detected, the
+ * driver should call blk_mq_quiesce_queue() to block new requests from
+ * dispatching, then blk_sync_queue() to halt any timeout work. When the
+ * hardware becomes operational again, the driver should call this function to
+ * reset previously dispatched request timers who's processing had been paused
+ * by the hardware, then call blk_mq_unquiesce_queue() to unblock future
+ * dispatch.
+ */
+void blk_mq_reset_rqs(struct request_queue *q)
+{
+	if (WARN_ON(!blk_queue_quiesced(q)))
+		return;
+	blk_mq_queue_tag_busy_iter(q, blk_mq_reset_rq, NULL);
+}
+EXPORT_SYMBOL_GPL(blk_mq_reset_rqs);
+
 struct flush_busy_ctx_data {
 	struct blk_mq_hw_ctx *hctx;
 	struct list_head *list;
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 15d1aa53d96c..28c421ba5094 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -327,6 +327,7 @@ void blk_freeze_queue_start(struct request_queue *q);
 void blk_mq_freeze_queue_wait(struct request_queue *q);
 int blk_mq_freeze_queue_wait_timeout(struct request_queue *q,
 				     unsigned long timeout);
+void blk_mq_reset_rqs(struct request_queue *q);
 
 int blk_mq_map_queues(struct blk_mq_queue_map *qmap);
 void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues);
-- 
2.14.4