Subject: [net-next 06/14] net/mlx5e: Avoid false lock depenency warning on tc_ht

From: Saeed Mahameed <[email-masked]>
Date: Mon, 1 Feb 2021 22:54:49 -0800

From: Roi Dayan <[email-masked]>

To avoid false lock dependency warning set the tc_ht lock
class different than the lock class of the ht being used when deleting
last flow from a group and then deleting a group, we get into del_sw_flow_group()
which call rhashtable_destroy on fg->ftes_hash which will take ht->mutex but
it's different than the ht->mutex here.

======================================================
WARNING: possible circular locking dependency detected
5.11.0-rc4_net_next_mlx5_949fdcc #1 Not tainted
------------------------------------------------------
modprobe/12950 is trying to acquire lock:
ffff88816510f910 (&node->lock){++++}-{3:3}, at: mlx5_del_flow_rules+0x2a/0x210 [mlx5_core]

but task is already holding lock:
ffff88815834e3e8 (&ht->mutex){+.+.}-{3:3}, at: rhashtable_free_and_destroy+0x37/0x340

which lock already depends on the new lock.

Signed-off-by: Roi Dayan <[email-masked]>
Signed-off-by: Saeed Mahameed <[email-masked]>
---
 drivers/net/ethernet/mellanox/mlx5/core/en_tc.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_tc.c b/drivers/net/ethernet/mellanox/mlx5/core/en_tc.c
index 8fd38ad8113b..280ea1e1e039 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_tc.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_tc.c
@@ -190,6 +190,14 @@ struct mlx5e_tc_attr_to_reg_mapping mlx5e_tc_attr_to_reg_mappings[] = {
 	[NIC_ZONE_RESTORE_TO_REG] = nic_zone_restore_to_reg_ct,
 };
 
+/* To avoid false lock dependency warning set the tc_ht lock
+ * class different than the lock class of the ht being used when deleting
+ * last flow from a group and then deleting a group, we get into del_sw_flow_group()
+ * which call rhashtable_destroy on fg->ftes_hash which will take ht->mutex but
+ * it's different than the ht->mutex here.
+ */
+static struct lock_class_key tc_ht_lock_key;
+
 static void mlx5e_put_flow_tunnel_id(struct mlx5e_tc_flow *flow);
 
 void
@@ -5215,6 +5223,8 @@ int mlx5e_tc_nic_init(struct mlx5e_priv *priv)
 	if (err)
 		return err;
 
+	lockdep_set_class(&tc->ht.mutex, &tc_ht_lock_key);
+
 	if (MLX5_CAP_FLOWTABLE_NIC_RX(priv->mdev, ignore_flow_level)) {
 		attr.flags = MLX5_CHAINS_AND_PRIOS_SUPPORTED |
 			MLX5_CHAINS_IGNORE_FLOW_LEVEL_SUPPORTED;
@@ -5333,6 +5343,8 @@ int mlx5e_tc_esw_init(struct rhashtable *tc_ht)
 	if (err)
 		goto err_ht_init;
 
+	lockdep_set_class(&tc_ht->mutex, &tc_ht_lock_key);
+
 	return err;
 
 err_ht_init:
-- 
2.29.2