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Subject[PATCH] net: dsa: Fix lockdep false positive splat
Date
Creating a macvtap on a DSA-backed interface results in the following
splat when lockdep is enabled:

[ 19.638080] IPv6: ADDRCONF(NETDEV_CHANGE): lan0: link becomes ready
[ 23.041198] device lan0 entered promiscuous mode
[ 23.043445] device eth0 entered promiscuous mode
[ 23.049255]
[ 23.049557] ============================================
[ 23.055021] WARNING: possible recursive locking detected
[ 23.060490] 5.0.0-rc3-00013-g56c857a1b8d3 #118 Not tainted
[ 23.066132] --------------------------------------------
[ 23.071598] ip/2861 is trying to acquire lock:
[ 23.076171] 00000000f61990cb (_xmit_ETHER){+...}, at: dev_set_rx_mode+0x1c/0x38
[ 23.083693]
[ 23.083693] but task is already holding lock:
[ 23.089696] 00000000ecf0c3b4 (_xmit_ETHER){+...}, at: dev_uc_add+0x24/0x70
[ 23.096774]
[ 23.096774] other info that might help us debug this:
[ 23.103494] Possible unsafe locking scenario:
[ 23.103494]
[ 23.109584] CPU0
[ 23.112093] ----
[ 23.114601] lock(_xmit_ETHER);
[ 23.117917] lock(_xmit_ETHER);
[ 23.121233]
[ 23.121233] *** DEADLOCK ***
[ 23.121233]
[ 23.127325] May be due to missing lock nesting notation
[ 23.127325]
[ 23.134315] 2 locks held by ip/2861:
[ 23.137987] #0: 000000003b766c72 (rtnl_mutex){+.+.}, at: rtnetlink_rcv_msg+0x338/0x4e0
[ 23.146231] #1: 00000000ecf0c3b4 (_xmit_ETHER){+...}, at: dev_uc_add+0x24/0x70
[ 23.153757]
[ 23.153757] stack backtrace:
[ 23.158243] CPU: 0 PID: 2861 Comm: ip Not tainted 5.0.0-rc3-00013-g56c857a1b8d3 #118
[ 23.166212] Hardware name: Globalscale Marvell ESPRESSOBin Board (DT)
[ 23.172843] Call trace:
[ 23.175358] dump_backtrace+0x0/0x188
[ 23.179116] show_stack+0x14/0x20
[ 23.182524] dump_stack+0xb4/0xec
[ 23.185928] __lock_acquire+0x123c/0x1860
[ 23.190048] lock_acquire+0xc8/0x248
[ 23.193724] _raw_spin_lock_bh+0x40/0x58
[ 23.197755] dev_set_rx_mode+0x1c/0x38
[ 23.201607] dev_set_promiscuity+0x3c/0x50
[ 23.205820] dsa_slave_change_rx_flags+0x5c/0x70
[ 23.210567] __dev_set_promiscuity+0x148/0x1e0
[ 23.215136] __dev_set_rx_mode+0x74/0x98
[ 23.219167] dev_uc_add+0x54/0x70
[ 23.222575] macvlan_open+0x170/0x1d0
[ 23.226336] __dev_open+0xe0/0x160
[ 23.229830] __dev_change_flags+0x16c/0x1b8
[ 23.234132] dev_change_flags+0x20/0x60
[ 23.238074] do_setlink+0x2d0/0xc50
[ 23.241658] __rtnl_newlink+0x5f8/0x6e8
[ 23.245601] rtnl_newlink+0x50/0x78
[ 23.249184] rtnetlink_rcv_msg+0x360/0x4e0
[ 23.253397] netlink_rcv_skb+0xe8/0x130
[ 23.257338] rtnetlink_rcv+0x14/0x20
[ 23.261012] netlink_unicast+0x190/0x210
[ 23.265043] netlink_sendmsg+0x288/0x350
[ 23.269075] sock_sendmsg+0x18/0x30
[ 23.272659] ___sys_sendmsg+0x29c/0x2c8
[ 23.276602] __sys_sendmsg+0x60/0xb8
[ 23.280276] __arm64_sys_sendmsg+0x1c/0x28
[ 23.284488] el0_svc_common+0xd8/0x138
[ 23.288340] el0_svc_handler+0x24/0x80
[ 23.292192] el0_svc+0x8/0xc

This looks fairly harmless (no actual deadlock occurs), and is
fixed in a similar way to c6894dec8ea9 ("bridge: fix lockdep
addr_list_lock false positive splat") by putting the addr_list_lock
in its own lockdep class.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
net/dsa/master.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/net/dsa/master.c b/net/dsa/master.c
index 71bb15f491c8..54f5551fb799 100644
--- a/net/dsa/master.c
+++ b/net/dsa/master.c
@@ -205,6 +205,8 @@ static void dsa_master_reset_mtu(struct net_device *dev)
rtnl_unlock();
}

+static struct lock_class_key dsa_master_addr_list_lock_key;
+
int dsa_master_setup(struct net_device *dev, struct dsa_port *cpu_dp)
{
int ret;
@@ -218,6 +220,8 @@ int dsa_master_setup(struct net_device *dev, struct dsa_port *cpu_dp)
wmb();

dev->dsa_ptr = cpu_dp;
+ lockdep_set_class(&dev->addr_list_lock,
+ &dsa_master_addr_list_lock_key);

ret = dsa_master_ethtool_setup(dev);
if (ret)
--
2.20.1
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