From: Vladimir Oltean olteanv@gmail.com
[ Upstream commit 2f1e8ea726e9020e01e9e2ae29c2d5eb11133032 ]
Since commit 845e0ebb4408 ("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: 845e0ebb4408 ("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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/dsa/slave.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-)
--- a/net/dsa/slave.c +++ b/net/dsa/slave.c @@ -1801,15 +1801,27 @@ int dsa_slave_create(struct dsa_port *po
dsa_slave_notify(slave_dev, DSA_PORT_REGISTER);
- ret = register_netdev(slave_dev); + rtnl_lock(); + + ret = register_netdevice(slave_dev); if (ret) { netdev_err(master, "error %d registering interface %s\n", ret, slave_dev->name); + rtnl_unlock(); goto out_phy; }
+ ret = netdev_upper_dev_link(master, slave_dev, NULL); + + rtnl_unlock(); + + if (ret) + goto out_unregister; + return 0;
+out_unregister: + unregister_netdev(slave_dev); out_phy: rtnl_lock(); phylink_disconnect_phy(p->dp->pl); @@ -1826,16 +1838,18 @@ out_free:
void dsa_slave_destroy(struct net_device *slave_dev) { + struct net_device *master = dsa_slave_to_master(slave_dev); struct dsa_port *dp = dsa_slave_to_port(slave_dev); struct dsa_slave_priv *p = netdev_priv(slave_dev);
netif_carrier_off(slave_dev); rtnl_lock(); + netdev_upper_dev_unlink(master, slave_dev); + unregister_netdevice(slave_dev); phylink_disconnect_phy(dp->pl); rtnl_unlock();
dsa_slave_notify(slave_dev, DSA_PORT_UNREGISTER); - unregister_netdev(slave_dev); phylink_destroy(dp->pl); gro_cells_destroy(&p->gcells); free_percpu(p->stats64);