[PATCH-4.5-v3 2/5] NVMe: Fix namespace removal deadlock

[keith.busch@intel.com (Keith Busch)]

This patch makes nvme namespace removal lockless. It is up to the caller
to ensure no active namespace scanning is occuring.

The lockless removal allows the driver to cleanup a namespace
request_queue if the controller fails during removal. Previously this
could deadlock trying to acquire the namespace mutex in order to handle
such events.

Signed-off-by: Keith Busch <keith.busch at intel.com>
---
 drivers/nvme/host/core.c | 15 +++++++++------
 drivers/nvme/host/nvme.h |  4 ++++
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 3cd921e..1b7387d 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -48,6 +48,10 @@ static void nvme_free_ns(struct kref *kref)
 {
 	struct nvme_ns *ns = container_of(kref, struct nvme_ns, kref);
 
+	mutex_lock(&ns->ctrl->namespaces_mutex);
+	list_del_init(&ns->list);
+	mutex_unlock(&ns->ctrl->namespaces_mutex);
+
 	if (ns->type == NVME_NS_LIGHTNVM)
 		nvme_nvm_unregister(ns->queue, ns->disk->disk_name);
 
@@ -1179,11 +1183,13 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid)
 
 static void nvme_ns_remove(struct nvme_ns *ns)
 {
-	bool kill = nvme_io_incapable(ns->ctrl) &&
-			!blk_queue_dying(ns->queue);
+	bool kill;
 
-	lockdep_assert_held(&ns->ctrl->namespaces_mutex);
+	if (test_and_set_bit(NVME_NS_REMOVING, &ns->flags))
+		return;
 
+	kill = nvme_io_incapable(ns->ctrl) &&
+			!blk_queue_dying(ns->queue);
 	if (kill) {
 		blk_set_queue_dying(ns->queue);
 
@@ -1206,7 +1212,6 @@ static void nvme_ns_remove(struct nvme_ns *ns)
 		blk_mq_abort_requeue_list(ns->queue);
 		blk_cleanup_queue(ns->queue);
 	}
-	list_del_init(&ns->list);
 	nvme_put_ns(ns);
 }
 
@@ -1300,10 +1305,8 @@ void nvme_remove_namespaces(struct nvme_ctrl *ctrl)
 {
 	struct nvme_ns *ns, *next;
 
-	mutex_lock(&ctrl->namespaces_mutex);
 	list_for_each_entry_safe(ns, next, &ctrl->namespaces, list)
 		nvme_ns_remove(ns);
-	mutex_unlock(&ctrl->namespaces_mutex);
 }
 
 static DEFINE_IDA(nvme_instance_ida);
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 9664d07..db413a7 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -112,6 +112,10 @@ struct nvme_ns {
 	bool ext;
 	u8 pi_type;
 	int type;
+	unsigned long flags;
+
+#define NVME_NS_REMOVING 0
+
 	u64 mode_select_num_blocks;
 	u32 mode_select_block_len;
 };
-- 
2.6.2.307.g37023ba