[PATCH 13/15] nvme: add Clang context annotations in rdma.c

[Nilay Shroff]

The device_list and nvme_rdma_device::entry are protected by
device_list_mutex. Annotate both with __guarded_by() so that Clang's
context analysis can validate accesses against the corresponding
locking requirements.

Similarly, nvme_rdma_ctrl_list and nvme_rdma_ctrl::list are protected
by nvme_rdma_ctrl_mutex. Annotate them with
__guarded_by(&nvme_rdma_ctrl_mutex).

It is safe to initialize nvme_rdma_ctrl::list while allocating the
controller object because the list entry has not yet been added to
nvme_rdma_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/rdma.c:972:24: warning: passing pointer to variable 'list' requires holding mutex 'nvme_rdma_ctrl_mutex'
      [-Wthread-safety-pointer]
  972 |         if (list_empty(&ctrl->list))
      |                               ^

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

Signed-off-by: Nilay Shroff <nilay at linux.ibm.com>
---
 drivers/nvme/host/rdma.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c
index f77c960f7632..a50efe3709d8 100644
--- a/drivers/nvme/host/rdma.c
+++ b/drivers/nvme/host/rdma.c
@@ -39,11 +39,17 @@
 #define NVME_RDMA_METADATA_SGL_SIZE \
 	(sizeof(struct scatterlist) * NVME_INLINE_METADATA_SG_CNT)
 
+static DEFINE_MUTEX(device_list_mutex);
+static __guarded_by(&device_list_mutex) LIST_HEAD(device_list);
+
+static DEFINE_MUTEX(nvme_rdma_ctrl_mutex);
+static __guarded_by(&nvme_rdma_ctrl_mutex) LIST_HEAD(nvme_rdma_ctrl_list);
+
 struct nvme_rdma_device {
 	struct ib_device	*dev;
 	struct ib_pd		*pd;
 	struct kref		ref;
-	struct list_head	entry;
+	struct list_head	entry __guarded_by(&device_list_mutex);
 	unsigned int		num_inline_segments;
 };
 
@@ -112,7 +118,7 @@ struct nvme_rdma_ctrl {
 
 	struct delayed_work	reconnect_work;
 
-	struct list_head	list;
+	struct list_head	list __guarded_by(&nvme_rdma_ctrl_mutex);
 
 	struct blk_mq_tag_set	admin_tag_set;
 	struct nvme_rdma_device	*device;
@@ -132,12 +138,6 @@ static inline struct nvme_rdma_ctrl *to_rdma_ctrl(struct nvme_ctrl *ctrl)
 	return container_of(ctrl, struct nvme_rdma_ctrl, ctrl);
 }
 
-static LIST_HEAD(device_list);
-static DEFINE_MUTEX(device_list_mutex);
-
-static LIST_HEAD(nvme_rdma_ctrl_list);
-static DEFINE_MUTEX(nvme_rdma_ctrl_mutex);
-
 /*
  * Disabling this option makes small I/O goes faster, but is fundamentally
  * unsafe.  With it turned off we will have to register a global rkey that
@@ -969,10 +969,12 @@ static void nvme_rdma_free_ctrl(struct nvme_ctrl *nctrl)
 {
 	struct nvme_rdma_ctrl *ctrl = to_rdma_ctrl(nctrl);
 
-	if (list_empty(&ctrl->list))
-		goto free_ctrl;
 
 	mutex_lock(&nvme_rdma_ctrl_mutex);
+	if (list_empty(&ctrl->list)) {
+		mutex_unlock(&nvme_rdma_ctrl_mutex);
+		goto free_ctrl;
+	}
 	list_del(&ctrl->list);
 	mutex_unlock(&nvme_rdma_ctrl_mutex);
 
@@ -2252,7 +2254,10 @@ static struct nvme_rdma_ctrl *nvme_rdma_alloc_ctrl(struct device *dev,
 	if (!ctrl)
 		return ERR_PTR(-ENOMEM);
 	ctrl->ctrl.opts = opts;
-	INIT_LIST_HEAD(&ctrl->list);
+	/*
+	 * Safe to init list while allocating ctrl object.
+	 */
+	context_unsafe(INIT_LIST_HEAD(&ctrl->list));
 
 	if (!(opts->mask & NVMF_OPT_TRSVCID)) {
 		opts->trsvcid =
-- 
2.53.0