[PATCH 2/3 Xenial SRU] nvme: fix max_segments integer truncation

[Tim Gardner]

From: Christoph Hellwig <hch at lst.de>

BugLink: http://bugs.launchpad.net/bugs/1588449

The block layer uses an unsigned short for max_segments.  The way we
calculate the value for NVMe tends to generate very large 32-bit values,
which after integer truncation may lead to a zero value instead of
the desired outcome.

Signed-off-by: Christoph Hellwig <hch at lst.de>
Reported-by: Jeff Lien <Jeff.Lien at hgst.com>
Tested-by: Jeff Lien <Jeff.Lien at hgst.com>
Reviewed-by: Keith Busch <keith.busch at intel.com>
Signed-off-by: Jens Axboe <axboe at fb.com>
(cherry picked from commit 45686b6198bd824f083ff5293f191d78db9d708a)
Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
---
 drivers/nvme/host/core.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index fde3b4a..6ab452d 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -839,9 +839,11 @@ static void nvme_set_queue_limits(struct nvme_ctrl *ctrl,
 		struct request_queue *q)
 {
 	if (ctrl->max_hw_sectors) {
+		u32 max_segments =
+			(ctrl->max_hw_sectors / (ctrl->page_size >> 9)) + 1;
+
 		blk_queue_max_hw_sectors(q, ctrl->max_hw_sectors);
-		blk_queue_max_segments(q,
-			(ctrl->max_hw_sectors / (ctrl->page_size >> 9)) + 1);
+		blk_queue_max_segments(q, min_t(u32, max_segments, USHRT_MAX));
 	}
 	if (ctrl->stripe_size)
 		blk_queue_chunk_sectors(q, ctrl->stripe_size >> 9);
-- 
1.9.1