nvme: fix panic if we boot w/o a namespace

If we format a drive, and then crash, we'll come back up. nvme_sim_ns
device won't attach because we don't have a namespace. Some drives (all?
I couldn't find it in the standard) send an AER with a namespace change,
which causes a NULL dereference because s_sim wasn't initialized because
we didn't attach. So, if we get into the ns_changed routine, bail early
if we didn't attach. We'll attach later, and deal with the ns correctly
if it's really there, or not attach one if it's not.

Sponsored by:		Netflix

1 files changed, 10 insertions, 0 deletions

diff --git a/sys/dev/nvme/nvme_sim.c b/sys/dev/nvme/nvme_sim.c
index 8b861cf3aa71..a59823847c39 100644
--- a/sys/dev/nvme/nvme_sim.c
+++ b/sys/dev/nvme/nvme_sim.c
@@ -406,6 +406,16 @@ nvme_sim_ns_added(device_t dev, struct nvme_namespace *ns)
 	union ccb *ccb;
 
 	/*
+	 * If we have no namespaces, then we both do not attach the nvme_sim_ns
+	 * device. And then get a ns changed AER as well to tell us about it
+	 * (which is how we get here). If there's no device attached, then
+	 * there's nothing to do. sc->s_sim will be NULL as well (since it
+	 * only gets set when we attach).
+	 */
+	if (!device_is_attached(dev))
+		return (0);
+
+	/*
 	 * We map the NVMe namespace idea onto the CAM unit LUN. For each new
 	 * namespace, scan or rescan the path to enumerate it.
 	 */