[PATCH v2 1/2] nvmet: defer setting ns->enabled to false in nvmet_ns_disable()

[Nilay Shroff <nilay@linux.ibm.com>]

nvmet_ns_disable() currently clears ns->enabled before draining
in-flight I/O references. This allows namespace configuration to be
changed while existing I/O requests can still hold a reference to the
namespace.

This can race with configuration of namespace attributes such as the
device path, UUID, NGUID etc. These attributes can be accessed by I/O
requests without holding subsys->lock and must not be modified while
such requests are still using the namespace.

In nvmet_ns_disable(), keep ns->enabled set while existing namespace
references are being drained, so namespace configuration remains blocked
until all in-flight I/O has completed. Set ns->enabled to false only
after the namespace references have been drained and the namespace
device has been disabled.

Introduce the NVMET_NS_IO_LIVE flag, which is set after the namespace
is successfully enabled in nvmet_ns_enable(). When nvmet_ns_disable()
starts, clear NVMET_NS_IO_LIVE so that the I/O path stops admitting new
I/O once the flag is cleared. Using test_and_clear_bit() in
nvmet_ns_disable() also prevents concurrent callers from starting a
second disable operation.

Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
---
 drivers/nvme/target/core.c  | 12 +++++++-----
 drivers/nvme/target/nvmet.h |  2 ++
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c
index 43871a8f56ca..1d4b4936bcac 100644
--- a/drivers/nvme/target/core.c
+++ b/drivers/nvme/target/core.c
@@ -448,7 +448,8 @@ u16 nvmet_req_find_ns(struct nvmet_req *req)
 	struct nvmet_subsys *subsys = nvmet_req_subsys(req);
 
 	req->ns = xa_load(&subsys->namespaces, nsid);
-	if (unlikely(!req->ns || !req->ns->enabled)) {
+	if (unlikely(!req->ns) ||
+	    !test_bit(NVMET_NS_IO_LIVE, &req->ns->flags)) {
 		req->error_loc = offsetof(struct nvme_common_command, nsid);
 		if (!req->ns) /* ns doesn't exist! */
 			return NVME_SC_INVALID_NS | NVME_STATUS_DNR;
@@ -623,6 +624,7 @@ int nvmet_ns_enable(struct nvmet_ns *ns)
 	ns->enabled = true;
 	xa_set_mark(&subsys->namespaces, ns->nsid, NVMET_NS_ENABLED);
 	nvmet_debugfs_ns_setup(ns);
+	set_bit(NVMET_NS_IO_LIVE, &ns->flags);
 	ret = 0;
 out_unlock:
 	mutex_unlock(&subsys->lock);
@@ -643,11 +645,11 @@ void nvmet_ns_disable(struct nvmet_ns *ns)
 	struct nvmet_subsys *subsys = ns->subsys;
 	struct nvmet_ctrl *ctrl;
 
+	if (!test_and_clear_bit(NVMET_NS_IO_LIVE, &ns->flags))
+		return;
+
 	mutex_lock(&subsys->lock);
-	if (!ns->enabled)
-		goto out_unlock;
 
-	ns->enabled = false;
 	xa_clear_mark(&subsys->namespaces, ns->nsid, NVMET_NS_ENABLED);
 	nvmet_debugfs_ns_free(ns);
 
@@ -675,7 +677,7 @@ void nvmet_ns_disable(struct nvmet_ns *ns)
 	mutex_lock(&subsys->lock);
 	nvmet_ns_changed(subsys, ns->nsid);
 	nvmet_ns_dev_disable(ns);
-out_unlock:
+	ns->enabled = false;
 	mutex_unlock(&subsys->lock);
 }
 
diff --git a/drivers/nvme/target/nvmet.h b/drivers/nvme/target/nvmet.h
index dbda55895f4f..162e2fdd848e 100644
--- a/drivers/nvme/target/nvmet.h
+++ b/drivers/nvme/target/nvmet.h
@@ -112,6 +112,8 @@ struct nvmet_ns {
 
 	bool			buffered_io;
 	bool			enabled;
+#define NVMET_NS_IO_LIVE	0
+	unsigned long		flags;
 	struct nvmet_subsys	*subsys;
 	const char		*device_path;
 
-- 
2.53.0