From: James Smart <jsmart2021@gmail.com>
Date: Wed, 18 Oct 2017 14:33:59 -0700
Subject: nvmet: synchronize sqhd update
Patch-mainline: v4.14-rc7
Git-commit: f9cf2a64912d67c9cf49c316a0a0ada0ea7ed1da
References: FATE#323952, FATE#322506

In testing target io in read write mix, we did indeed get into cases where
sqhd didn't update properly and slowly missed enough updates to shutdown
the queue.

Protect the updating sqhd by using cmpxchg, and for that turn the sqhd
field into a u32 so that cmpxchg works on it for all architectures.

Signed-off-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Johannes Thumshirn <jthumshirn@suse.de>
---
 drivers/nvme/target/core.c  |   15 ++++++++++++---
 drivers/nvme/target/nvmet.h |    2 +-
 2 files changed, 13 insertions(+), 4 deletions(-)

--- a/drivers/nvme/target/core.c
+++ b/drivers/nvme/target/core.c
@@ -387,12 +387,21 @@ struct nvmet_ns *nvmet_ns_alloc(struct n
 
 static void __nvmet_req_complete(struct nvmet_req *req, u16 status)
 {
+	u32 old_sqhd, new_sqhd;
+	u16 sqhd;
+
 	if (status)
 		nvmet_set_status(req, status);
 
-	if (req->sq->size)
-		req->sq->sqhd = (req->sq->sqhd + 1) % req->sq->size;
-	req->rsp->sq_head = cpu_to_le16(req->sq->sqhd);
+	if (req->sq->size) {
+		do {
+			old_sqhd = req->sq->sqhd;
+			new_sqhd = (old_sqhd + 1) % req->sq->size;
+		} while (cmpxchg(&req->sq->sqhd, old_sqhd, new_sqhd) !=
+					old_sqhd);
+	}
+	sqhd = req->sq->sqhd & 0x0000FFFF;
+	req->rsp->sq_head = cpu_to_le16(sqhd);
 	req->rsp->sq_id = cpu_to_le16(req->sq->qid);
 	req->rsp->command_id = req->cmd->common.command_id;
 
--- a/drivers/nvme/target/nvmet.h
+++ b/drivers/nvme/target/nvmet.h
@@ -74,7 +74,7 @@ struct nvmet_sq {
 	struct percpu_ref	ref;
 	u16			qid;
 	u16			size;
-	u16			sqhd;
+	u32			sqhd;
 	struct completion	free_done;
 	struct completion	confirm_done;
 };