[PATCH v3 net-next 3/6] vxlan: move VXLAN_F_MDB to struct vxlan_dev flags

[Eric Dumazet <edumazet@google.com>]

VXLAN_F_MDB is an internal runtime state flag indicating whether any
MDB entries are configured on the device, rather than a netlink
configuration attribute.

In preparation for converting vxlan->cfg to an RCU-protected pointer,
move VXLAN_F_MDB from struct vxlan_config to a dedicated 'flags' field
in struct vxlan_dev as VXLAN_DEV_F_MDB, using atomic bitops (set_bit(),
clear_bit(), test_bit()) to avoid KCSAN data races between the TX path
and RTNL operations.

This avoids having to dynamically reallocate and publish a new
vxlan_config structure via RCU whenever the first MDB entry is added
or the last one is removed, and prevents potential memory allocation
failures during MDB teardown under memory pressure.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 drivers/net/vxlan/vxlan_core.c | 2 +-
 drivers/net/vxlan/vxlan_mdb.c  | 6 +++---
 include/net/vxlan.h            | 6 +++++-
 3 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/net/vxlan/vxlan_core.c b/drivers/net/vxlan/vxlan_core.c
index 3115b056a68ddae35720bf6e25558b77f51beba0..4bb6e05379ca7835f355017c6cccd221c89c1f2c 100644
--- a/drivers/net/vxlan/vxlan_core.c
+++ b/drivers/net/vxlan/vxlan_core.c
@@ -2824,7 +2824,7 @@ static netdev_tx_t vxlan_xmit(struct sk_buff *skb, struct net_device *dev)
 	if (nhid)
 		return vxlan_xmit_nhid(skb, dev, nhid, vni, cfg);
 
-	if (flags & VXLAN_F_MDB) {
+	if (test_bit(VXLAN_DEV_F_MDB, &vxlan->flags)) {
 		struct vxlan_mdb_entry *mdb_entry;
 
 		rcu_read_lock();
diff --git a/drivers/net/vxlan/vxlan_mdb.c b/drivers/net/vxlan/vxlan_mdb.c
index 56ca9283283307d8b1231c3b26724474e6c838d6..cf606256d0929c4dd356ec8aa343150c10edfb82 100644
--- a/drivers/net/vxlan/vxlan_mdb.c
+++ b/drivers/net/vxlan/vxlan_mdb.c
@@ -1219,7 +1219,7 @@ vxlan_mdb_entry_get(struct vxlan_dev *vxlan,
 		goto err_free_entry;
 
 	if (hlist_is_singular_node(&mdb_entry->mdb_node, &vxlan->mdb_list))
-		vxlan->cfg.flags |= VXLAN_F_MDB;
+		set_bit(VXLAN_DEV_F_MDB, &vxlan->flags);
 
 	return mdb_entry;
 
@@ -1236,7 +1236,7 @@ static void vxlan_mdb_entry_put(struct vxlan_dev *vxlan,
 		return;
 
 	if (hlist_is_singular_node(&mdb_entry->mdb_node, &vxlan->mdb_list))
-		vxlan->cfg.flags &= ~VXLAN_F_MDB;
+		clear_bit(VXLAN_DEV_F_MDB, &vxlan->flags);
 
 	rhashtable_remove_fast(&vxlan->mdb_tbl, &mdb_entry->rhnode,
 			       vxlan_mdb_rht_params);
@@ -1762,7 +1762,7 @@ void vxlan_mdb_fini(struct vxlan_dev *vxlan)
 	struct vxlan_mdb_flush_desc desc = {};
 
 	vxlan_mdb_flush(vxlan, &desc);
-	WARN_ON_ONCE(vxlan->cfg.flags & VXLAN_F_MDB);
+	WARN_ON_ONCE(test_bit(VXLAN_DEV_F_MDB, &vxlan->flags));
 	rhashtable_free_and_destroy(&vxlan->mdb_tbl, vxlan_mdb_check_empty,
 				    NULL);
 }
diff --git a/include/net/vxlan.h b/include/net/vxlan.h
index 7b82075055237058d231d636698f640c75c521af..d323f91af2364822e148310297c978fec7664010 100644
--- a/include/net/vxlan.h
+++ b/include/net/vxlan.h
@@ -300,6 +300,7 @@ struct vxlan_dev {
 	spinlock_t	  hash_lock;
 	unsigned int	  addrcnt;
 	struct gro_cells  gro_cells;
+	unsigned long	  flags;
 
 	struct vxlan_config	cfg;
 
@@ -313,6 +314,10 @@ struct vxlan_dev {
 	unsigned int mdb_seq;
 };
 
+enum vxlan_dev_flags {
+	VXLAN_DEV_F_MDB,
+};
+
 #define VXLAN_F_LEARN			0x01
 #define VXLAN_F_PROXY			0x02
 #define VXLAN_F_RSC			0x04
@@ -331,7 +336,6 @@ struct vxlan_dev {
 #define VXLAN_F_IPV6_LINKLOCAL		0x8000
 #define VXLAN_F_TTL_INHERIT		0x10000
 #define VXLAN_F_VNIFILTER               0x20000
-#define VXLAN_F_MDB			0x40000
 #define VXLAN_F_LOCALBYPASS		0x80000
 #define VXLAN_F_MC_ROUTE		0x100000
 
-- 
2.55.0.1007.g17ff1f9808-goog