netdev - [net-next 07/15] net/mlx5e: CT, Avoid false lock dependency warning

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Date:   Thu, 11 Mar 2021 14:37:15 -0800
From:   Saeed Mahameed <saeed@...nel.org>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, Roi Dayan <roid@...dia.com>,
        Paul Blakey <paulb@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>
Subject: [net-next 07/15] net/mlx5e: CT, Avoid false lock dependency warning

From: Roi Dayan <roid@...dia.com>

To avoid false lock dependency warning set the ct_entries_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
5.10.0-rc2+ #8 Tainted: G           O
------------------------------------------------------
revalidator23/24009 is trying to acquire lock:
ffff888128d83828 (&node->lock){++++}-{3:3}, at: mlx5_del_flow_rules+0x83/0x7a0 [mlx5_core]

but task is already holding lock:
ffff8881081ef518 (&ht->mutex){+.+.}-{3:3}, at: rhashtable_free_and_destroy+0x37/0x720

which lock already depends on the new lock.

Signed-off-by: Roi Dayan <roid@...dia.com>
Reviewed-by: Paul Blakey <paulb@...dia.com>
Signed-off-by: Saeed Mahameed <saeedm@...dia.com>
---
 drivers/net/ethernet/mellanox/mlx5/core/en/tc_ct.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/tc_ct.c b/drivers/net/ethernet/mellanox/mlx5/core/en/tc_ct.c
index f3f6eb081948..f81da2dc6af1 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en/tc_ct.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en/tc_ct.c
@@ -1539,6 +1539,14 @@ mlx5_tc_ct_free_pre_ct_tables(struct mlx5_ct_ft *ft)
 	mlx5_tc_ct_free_pre_ct(ft, &ft->pre_ct);
 }
 
+/* To avoid false lock dependency warning set the ct_entries_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 ct_entries_ht_lock_key;
+
 static struct mlx5_ct_ft *
 mlx5_tc_ct_add_ft_cb(struct mlx5_tc_ct_priv *ct_priv, u16 zone,
 		     struct nf_flowtable *nf_ft)
@@ -1573,6 +1581,8 @@ mlx5_tc_ct_add_ft_cb(struct mlx5_tc_ct_priv *ct_priv, u16 zone,
 	if (err)
 		goto err_init;
 
+	lockdep_set_class(&ft->ct_entries_ht.mutex, &ct_entries_ht_lock_key);
+
 	err = rhashtable_insert_fast(&ct_priv->zone_ht, &ft->node,
 				     zone_params);
 	if (err)
-- 
2.29.2