[PATCH] nvmet: configfs: use ctrl->instance to track passthru subsystems

[Evan Burgess]

To prevent enabling more than one passthrough subsystem per NVMe 
controller, passthru.c maintains an xarray indexed by cntlid values.
Passthrough for a given nvmet subsystem cannot be enabled by configfs
if the subsystem's passthru_ctrl->cntlid value is already accounted
for in the xarray. 

However, according to the NVMe spec (rev 2.0c, p.145), "The Controller
ID (CNTLID) value returned in the Identify Controller data structure 
may be used to uniquely identify a controller within an NVM subsystem,"
meaning that cntlid values are not guaranteed to be globally unique 
across multiple subsystems. Instead, the cntlid only uniquely 
identifies multiple controllers _within_ a subsystem. 

As a result, multiple unique & valid NVMe targets can be blocked from 
enabling passthrough at the same time if their controllers share cntlid
values, a behavior allowed by the spec. Fix this by indexing the xarray 
with passthru_ctrl->instance values, which are allocated per 
controller by IDA and thus should be truly unique.
 
Reviewed-by: Sagi Grimberg <sagi at grimberg.me>
Signed-off-by: Evan Burgess <evan.burgess at seagate.com>
---
 drivers/nvme/target/passthru.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/nvme/target/passthru.c b/drivers/nvme/target/passthru.c
index 9fe07d7efa96..f2d963e1fe94 100644
--- a/drivers/nvme/target/passthru.c
+++ b/drivers/nvme/target/passthru.c
@@ -602,7 +602,7 @@ int nvmet_passthru_ctrl_enable(struct nvmet_subsys *subsys)
 		goto out_put_file;
 	}
 
-	old = xa_cmpxchg(&passthru_subsystems, ctrl->cntlid, NULL,
+	old = xa_cmpxchg(&passthru_subsystems, ctrl->instance, NULL,
 			 subsys, GFP_KERNEL);
 	if (xa_is_err(old)) {
 		ret = xa_err(old);
@@ -635,7 +635,7 @@ int nvmet_passthru_ctrl_enable(struct nvmet_subsys *subsys)
 static void __nvmet_passthru_ctrl_disable(struct nvmet_subsys *subsys)
 {
 	if (subsys->passthru_ctrl) {
-		xa_erase(&passthru_subsystems, subsys->passthru_ctrl->cntlid);
+		xa_erase(&passthru_subsystems, subsys->passthru_ctrl->instance);
 		module_put(subsys->passthru_ctrl->ops->module);
 		nvme_put_ctrl(subsys->passthru_ctrl);
 	}
-- 
2.34.1