[PATCH 14/15] nvme: add Clang context annotations in tcp.c

[Nilay Shroff]

The nvme_tcp_ctrl_list and nvme_tcp_ctrl::list are protected by
nvme_tcp_ctrl_mutex. Annotate both with
__guarded_by(&nvme_tcp_ctrl_mutex) so that Clang's context analysis
can validate accesses against the corresponding locking requirements.

It is safe to initialize nvme_tcp_ctrl::list while allocating the
controller object because the list entry has not yet been added to
nvme_tcp_ctrl_list. Annotate the initialization with context_unsafe()
to suppress the corresponding Clang warning.

After adding the above annotations, Clang reports the following
warning:
    drivers/nvme/host/tcp.c:2572:24: warning: passing pointer to variable 'list' requires holding mutex 'nvme_tcp_ctrl_mutex'
          [-Wthread-safety-pointer]
     2572 |         if (list_empty(&ctrl->list))
          |                               ^

Fix the warning by performing the list_empty() check while holding
nvme_tcp_ctrl_mutex.

Signed-off-by: Nilay Shroff <nilay at linux.ibm.com>
---
 drivers/nvme/host/tcp.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
index 68a1d7640494..86ef98aefeb4 100644
--- a/drivers/nvme/host/tcp.c
+++ b/drivers/nvme/host/tcp.c
@@ -182,13 +182,16 @@ struct nvme_tcp_queue {
 	void (*write_space)(struct sock *);
 };
 
+static DEFINE_MUTEX(nvme_tcp_ctrl_mutex);
+static __guarded_by(&nvme_tcp_ctrl_mutex) LIST_HEAD(nvme_tcp_ctrl_list);
+
 struct nvme_tcp_ctrl {
 	/* read only in the hot path */
 	struct nvme_tcp_queue	*queues;
 	struct blk_mq_tag_set	tag_set;
 
 	/* other member variables */
-	struct list_head	list;
+	struct list_head	list __guarded_by(&nvme_tcp_ctrl_mutex);
 	struct blk_mq_tag_set	admin_tag_set;
 	struct sockaddr_storage addr;
 	struct sockaddr_storage src_addr;
@@ -200,8 +203,6 @@ struct nvme_tcp_ctrl {
 	u32			io_queues[HCTX_MAX_TYPES];
 };
 
-static LIST_HEAD(nvme_tcp_ctrl_list);
-static DEFINE_MUTEX(nvme_tcp_ctrl_mutex);
 static struct workqueue_struct *nvme_tcp_wq;
 static const struct blk_mq_ops nvme_tcp_mq_ops;
 static const struct blk_mq_ops nvme_tcp_admin_mq_ops;
@@ -2568,10 +2569,11 @@ static void nvme_tcp_free_ctrl(struct nvme_ctrl *nctrl)
 {
 	struct nvme_tcp_ctrl *ctrl = to_tcp_ctrl(nctrl);
 
-	if (list_empty(&ctrl->list))
-		goto free_ctrl;
-
 	mutex_lock(&nvme_tcp_ctrl_mutex);
+	if (list_empty(&ctrl->list)) {
+		mutex_unlock(&nvme_tcp_ctrl_mutex);
+		goto free_ctrl;
+	}
 	list_del(&ctrl->list);
 	mutex_unlock(&nvme_tcp_ctrl_mutex);
 
@@ -2910,7 +2912,10 @@ static struct nvme_tcp_ctrl *nvme_tcp_alloc_ctrl(struct device *dev,
 	if (!ctrl)
 		return ERR_PTR(-ENOMEM);
 
-	INIT_LIST_HEAD(&ctrl->list);
+	/*
+	 * Safe to init list while allocating ctrl object.
+	 */
+	context_unsafe(INIT_LIST_HEAD(&ctrl->list));
 	ctrl->ctrl.opts = opts;
 	ctrl->ctrl.queue_count = opts->nr_io_queues + opts->nr_write_queues +
 				opts->nr_poll_queues + 1;
-- 
2.53.0