[PATCH net 2/4] net/mlx5: devcom, Base component size on linked devices

[Tariq Toukan]

From: Shay Drory <shayd@xxxxxxxxxx>

mlx5_devcom_comp_get_size() returns the component's kref count. That
kref is bumped in mlx5_devcom_register_component() under comp_list_lock,
before the comp_dev is linked onto comp_dev_list_head under comp->sem.
The event broadcast (mlx5_devcom_locked_send_event()) walks that list.

Hence, a caller can read the expected size, but send_event won't be sent
to all peers. In the SD group registration path, this lets a member
broadcast its role-election event over an incomplete list, electing a
primary that never completes the group, is never marked ready, and
leaves the group with a stale primary.

Track the number of linked comp_devs in a dedicated counter, maintained
under comp->sem together with the list add/remove, and return it from
mlx5_devcom_comp_get_size().

Fixes: 9bb1ac80738a ("net/mlx5: devcom, Add component size getter")
Signed-off-by: Shay Drory <shayd@xxxxxxxxxx>
Reviewed-by: Akiva Goldberger <agoldberger@xxxxxxxxxx>
Signed-off-by: Tariq Toukan <tariqt@xxxxxxxxxx>
---
 drivers/net/ethernet/mellanox/mlx5/core/lib/devcom.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lib/devcom.c b/drivers/net/ethernet/mellanox/mlx5/core/lib/devcom.c
index 64f92427602d..75855481522b 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/lib/devcom.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/lib/devcom.c
@@ -37,6 +37,7 @@ struct mlx5_devcom_comp {
 	struct mlx5_devcom_key key;
 	mlx5_devcom_event_handler_t handler;
 	struct kref ref;
+	int nr_devs;
 	bool ready;
 	struct rw_semaphore sem;
 	struct lock_class_key lock_key;
@@ -170,6 +171,7 @@ devcom_alloc_comp_dev(struct mlx5_devcom_dev *devc,
 
 	down_write(&comp->sem);
 	list_add_tail(&devcom->list, &comp->comp_dev_list_head);
+	WRITE_ONCE(comp->nr_devs, comp->nr_devs + 1);
 	up_write(&comp->sem);
 
 	return devcom;
@@ -182,6 +184,7 @@ devcom_free_comp_dev(struct mlx5_devcom_comp_dev *devcom)
 
 	down_write(&comp->sem);
 	list_del(&devcom->list);
+	WRITE_ONCE(comp->nr_devs, comp->nr_devs - 1);
 	up_write(&comp->sem);
 
 	kref_put(&devcom->devc->ref, mlx5_devcom_dev_release);
@@ -284,7 +287,7 @@ int mlx5_devcom_comp_get_size(struct mlx5_devcom_comp_dev *devcom)
 {
 	struct mlx5_devcom_comp *comp = devcom->comp;
 
-	return kref_read(&comp->ref);
+	return READ_ONCE(comp->nr_devs);
 }
 
 int mlx5_devcom_locked_send_event(struct mlx5_devcom_comp_dev *devcom,
-- 
2.44.0