[PATCHv2 3/3] nvme-pci: fix queue_rqs list splitting

[Keith Busch <kbusch@kernel.org>]

If command prep fails, current handling will orphan subsequent requests
in the list. Consider a simple example:

  rqlist = [ 1 -> 2 ]

When prep for request '1' fails, it will be appended to the
'requeue_list', leaving request '2' disconnected from the original
rqlist and no longer tracked. Meanwhile, rqlist is still pointing to the
failed request '1' and will attempt to submit an unprepped command.

Fix this by updating the rqlist accordingly using the request list
helper functions.

Fixes: d62cbcf62f2f ("nvme: add support for mq_ops->queue_rqs()")
Signed-off-by: Keith Busch <kbusch@kernel.org>
---
v1->v2:

  Replaced the backward looking iterator with the forward looking
  version implemented in PATCH 1/3. This is a little easier to read.

  Replaced the driver's list manipulation with the helper function
  provided in PATCH 2/3.

 drivers/nvme/host/pci.c | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 50deb8b69c40..992ee314e91b 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -999,30 +999,30 @@ static bool nvme_prep_rq_batch(struct nvme_queue *nvmeq, struct request *req)
 
 static void nvme_queue_rqs(struct request **rqlist)
 {
-	struct request *req = rq_list_peek(rqlist), *prev = NULL;
+	struct request *req, *next, *prev = NULL;
 	struct request *requeue_list = NULL;
 
-	do {
+	rq_list_for_each_safe(rqlist, req, next) {
 		struct nvme_queue *nvmeq = req->mq_hctx->driver_data;
 
 		if (!nvme_prep_rq_batch(nvmeq, req)) {
 			/* detach 'req' and add to remainder list */
-			if (prev)
-				prev->rq_next = req->rq_next;
-			rq_list_add(&requeue_list, req);
-		} else {
-			prev = req;
+			rq_list_move(rqlist, &requeue_list, req, prev, next);
+
+			req = prev;
+			if (!req)
+				continue;
 		}
 
-		req = rq_list_next(req);
-		if (!req || (prev && req->mq_hctx != prev->mq_hctx)) {
+		if (!next || req->mq_hctx != next->mq_hctx) {
 			/* detach rest of list, and submit */
-			if (prev)
-				prev->rq_next = NULL;
+			req->rq_next = NULL;
 			nvme_submit_cmds(nvmeq, rqlist);
-			*rqlist = req;
-		}
-	} while (req);
+			*rqlist = next;
+			prev = NULL;
+		} else
+			prev = req;
+	}
 
 	*rqlist = requeue_list;
 }
-- 
2.25.4