vxlan: move VXLAN_F_MDB to struct vxlan_dev flags

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.

mlxsw validates cfg->flags against a deny-by-default mask, so
VXLAN_F_MDB used to make mlxsw_sp_nve_vxlan_can_offload() reject a
device with MDB entries as carrying an unsupported flag. Add an
explicit VXLAN_DEV_F_MDB test there to keep that rejection, with a
message naming the actual reason.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260922181102.3989489-6-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions