Since commit 845e0ebb44 ("net: change addr_list_lock back to static
key"), cascaded DSA setups (DSA switch port as DSA master for another
DSA switch port) are emitting this lockdep warning:
============================================
WARNING: possible recursive locking detected
5.8.0-rc1-00133-g923e4b5032dd-dirty #208 Not tainted
--------------------------------------------
dhcpcd/323 is trying to acquire lock:
ffff000066dd4268 (&dsa_master_addr_list_lock_key/1){+...}-{2:2}, at: dev_mc_sync+0x44/0x90
but task is already holding lock:
ffff00006608c268 (&dsa_master_addr_list_lock_key/1){+...}-{2:2}, at: dev_mc_sync+0x44/0x90
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&dsa_master_addr_list_lock_key/1);
lock(&dsa_master_addr_list_lock_key/1);
*** DEADLOCK ***
May be due to missing lock nesting notation
3 locks held by dhcpcd/323:
#0: ffffdbd1381dda18 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_lock+0x24/0x30
#1: ffff00006614b268 (_xmit_ETHER){+...}-{2:2}, at: dev_set_rx_mode+0x28/0x48
#2: ffff00006608c268 (&dsa_master_addr_list_lock_key/1){+...}-{2:2}, at: dev_mc_sync+0x44/0x90
stack backtrace:
Call trace:
dump_backtrace+0x0/0x1e0
show_stack+0x20/0x30
dump_stack+0xec/0x158
__lock_acquire+0xca0/0x2398
lock_acquire+0xe8/0x440
_raw_spin_lock_nested+0x64/0x90
dev_mc_sync+0x44/0x90
dsa_slave_set_rx_mode+0x34/0x50
__dev_set_rx_mode+0x60/0xa0
dev_mc_sync+0x84/0x90
dsa_slave_set_rx_mode+0x34/0x50
__dev_set_rx_mode+0x60/0xa0
dev_set_rx_mode+0x30/0x48
__dev_open+0x10c/0x180
__dev_change_flags+0x170/0x1c8
dev_change_flags+0x2c/0x70
devinet_ioctl+0x774/0x878
inet_ioctl+0x348/0x3b0
sock_do_ioctl+0x50/0x310
sock_ioctl+0x1f8/0x580
ksys_ioctl+0xb0/0xf0
__arm64_sys_ioctl+0x28/0x38
el0_svc_common.constprop.0+0x7c/0x180
do_el0_svc+0x2c/0x98
el0_sync_handler+0x9c/0x1b8
el0_sync+0x158/0x180
Since DSA never made use of the netdev API for describing links between
upper devices and lower devices, the dev->lower_level value of a DSA
switch interface would be 1, which would warn when it is a DSA master.
We can use netdev_upper_dev_link() to describe the relationship between
a DSA slave and a DSA master. To be precise, a DSA "slave" (switch port)
is an "upper" to a DSA "master" (host port). The relationship is "many
uppers to one lower", like in the case of VLAN. So, for that reason, we
use the same function as VLAN uses.
There might be a chance that somebody will try to take hold of this
interface and use it immediately after register_netdev() and before
netdev_upper_dev_link(). To avoid that, we do the registration and
linkage while holding the RTNL, and we use the RTNL-locked cousin of
register_netdev(), which is register_netdevice().
Since this warning was not there when lockdep was using dynamic keys for
addr_list_lock, we are blaming the lockdep patch itself. The network
stack _has_ been using static lockdep keys before, and it _is_ likely
that stacked DSA setups have been triggering these lockdep warnings
since forever, however I can't test very old kernels on this particular
stacked DSA setup, to ensure I'm not in fact introducing regressions.
Fixes: 845e0ebb44 ("net: change addr_list_lock back to static key")
Suggested-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2f1e8ea726