Cited commit converted the neighbour code to use the standard RCU
variant instead of the RCU-bh variant, but the VRF code still uses
rcu_read_lock_bh() / rcu_read_unlock_bh() around the neighbour lookup
code in its IPv4 and IPv6 output paths, resulting in lockdep splats
[1][2]. Can be reproduced using [3].

Fix by switching to rcu_read_lock() / rcu_read_unlock().

[1]
=============================
WARNING: suspicious RCU usage
6.5.0-rc1-custom-g9c099e6dbf98 #403 Not tainted
-----------------------------
include/net/neighbour.h:302 suspicious rcu_dereference_check() usage!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1
2 locks held by ping/183:
 #0: ffff888105ea1d80 (sk_lock-AF_INET){+.+.}-{0:0}, at: raw_sendmsg+0xc6c/0x33c0
 #1: ffffffff85b46820 (rcu_read_lock_bh){....}-{1:2}, at: vrf_output+0x2e3/0x2030

stack backtrace:
CPU: 0 PID: 183 Comm: ping Not tainted 6.5.0-rc1-custom-g9c099e6dbf98 #403
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-1.fc37 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xc1/0xf0
 lockdep_rcu_suspicious+0x211/0x3b0
 vrf_output+0x1380/0x2030
 ip_push_pending_frames+0x125/0x2a0
 raw_sendmsg+0x200d/0x33c0
 inet_sendmsg+0xa2/0xe0
 __sys_sendto+0x2aa/0x420
 __x64_sys_sendto+0xe5/0x1c0
 do_syscall_64+0x38/0x80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

[2]
=============================
WARNING: suspicious RCU usage
6.5.0-rc1-custom-g9c099e6dbf98 #403 Not tainted
-----------------------------
include/net/neighbour.h:302 suspicious rcu_dereference_check() usage!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1
2 locks held by ping6/182:
 #0: ffff888114b63000 (sk_lock-AF_INET6){+.+.}-{0:0}, at: rawv6_sendmsg+0x1602/0x3e50
 #1: ffffffff85b46820 (rcu_read_lock_bh){....}-{1:2}, at: vrf_output6+0xe9/0x1310

stack backtrace:
CPU: 0 PID: 182 Comm: ping6 Not tainted 6.5.0-rc1-custom-g9c099e6dbf98 #403
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-1.fc37 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xc1/0xf0
 lockdep_rcu_suspicious+0x211/0x3b0
 vrf_output6+0xd32/0x1310
 ip6_local_out+0xb4/0x1a0
 ip6_send_skb+0xbc/0x340
 ip6_push_pending_frames+0xe5/0x110
 rawv6_sendmsg+0x2e6e/0x3e50
 inet_sendmsg+0xa2/0xe0
 __sys_sendto+0x2aa/0x420
 __x64_sys_sendto+0xe5/0x1c0
 do_syscall_64+0x38/0x80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

[3]
#!/bin/bash

ip link add name vrf-red up numtxqueues 2 type vrf table 10
ip link add name swp1 up master vrf-red type dummy
ip address add 192.0.2.1/24 dev swp1
ip address add 2001:db8:1::1/64 dev swp1
ip neigh add 192.0.2.2 lladdr 00:11:22:33:44:55 nud perm dev swp1
ip neigh add 2001:db8:1::2 lladdr 00:11:22:33:44:55 nud perm dev swp1
ip vrf exec vrf-red ping 192.0.2.2 -c 1 &> /dev/null
ip vrf exec vrf-red ping6 2001:db8:1::2 -c 1 &> /dev/null

Fixes: 09eed11 ("neighbour: switch to standard rcu, instead of rcu_bh")
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Link: https://lore.kernel.org/netdev/CA+G9fYtEr-=GbcXNDYo3XOkwR+uYgehVoDjsP0pFLUpZ_AZcyg@mail.gmail.com/
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230715153605.4068066-1-idosch@nvidia.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>