[PATCH 02/23] nvmet: fix nvmet_ns::bdev access using nvmet_subsys::lock

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

nvmet_get_smart_log_all() iterates over enabled namespaces and accesses
ns->bdev to collect block device statistics without holding
nvmet_subsys::lock.

Since nvmet_ns::bdev is annotated with __guarded_by(&subsys->lock), the
clang context analyzer reports this access as a locking violation:

drivers/nvme/target/admin-cmd.c:274:12: error: reading variable 'bdev' requires holding mutex 'ns->subsys->lock' [-Werror,-Wthread-safety-precise]
  274 |                 if (!ns->bdev)
      |                          ^

Fix this by acquiring ctrl->subsys->lock while iterating over the
enabled namespaces and accessing their block device statistics.

Since ctrl->subsys->lock and ns->subsys->lock refer to the same lock,
explicitly use __assume_ctx_lock() to inform the clang context analyzer
of the corresponding locking capability.

Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
---
 drivers/nvme/target/admin-cmd.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/nvme/target/admin-cmd.c b/drivers/nvme/target/admin-cmd.c
index 2d4e21b3ee7d..517f8cc78473 100644
--- a/drivers/nvme/target/admin-cmd.c
+++ b/drivers/nvme/target/admin-cmd.c
@@ -289,7 +289,15 @@ static u16 nvmet_get_smart_log_all(struct nvmet_req *req,
 	unsigned long idx;
 
 	ctrl = req->sq->ctrl;
+	mutex_lock(&ctrl->subsys->lock);
 	nvmet_for_each_enabled_ns(&ctrl->subsys->namespaces, idx, ns) {
+		/*
+		 * Both ctrl->subsys->lock and ns->subsys->lock refer to the
+		 * same lock. However there's no way for us to annotate such
+		 * locking semantics using clang context annotation. So
+		 * explicitly assert the capability.
+		 */
+		__assume_ctx_lock(&ns->subsys->lock);
 		/* we don't have the right data for file backed ns */
 		if (!ns->bdev)
 			continue;
@@ -300,6 +308,7 @@ static u16 nvmet_get_smart_log_all(struct nvmet_req *req,
 		data_units_written += DIV_ROUND_UP(
 			part_stat_read(ns->bdev, sectors[WRITE]), 1000);
 	}
+	mutex_unlock(&ctrl->subsys->lock);
 
 	put_unaligned_le64(host_reads, &slog->host_reads[0]);
 	put_unaligned_le64(data_units_read, &slog->data_units_read[0]);
-- 
2.53.0