Re: [syzbot] [net?] WARNING in nsim_fib_event_nb

[syzbot <syzbot+a259a17220263c2d73fc@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
unregister_netdevice: waiting for DEV to become free

unregister_netdevice: waiting for lo to become free. Usage count = 601
ref_tracker: lo@ffff888031d42610 has 600/600 users at
     __netdev_tracker_alloc include/linux/netdevice.h:4330 [inline]
     netdev_tracker_alloc include/linux/netdevice.h:4342 [inline]
     netdev_get_by_index+0x79/0xb0 net/core/dev.c:1006
     fib6_nh_init+0x1c4/0x2030 net/ipv6/route.c:3590
     ip6_route_info_create_nh+0x139/0x870 net/ipv6/route.c:3866
     ip6_route_mpath_info_create_nh net/ipv6/route.c:5429 [inline]
     ip6_route_multipath_add net/ipv6/route.c:5544 [inline]
     inet6_rtm_newroute+0x8ca/0x1d90 net/ipv6/route.c:5729
     rtnetlink_rcv_msg+0x7cc/0xb70 net/core/rtnetlink.c:6955
     netlink_rcv_skb+0x219/0x490 net/netlink/af_netlink.c:2534
     netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
     netlink_unicast+0x758/0x8d0 net/netlink/af_netlink.c:1339
     netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1883
     sock_sendmsg_nosec net/socket.c:712 [inline]
     __sock_sendmsg+0x219/0x270 net/socket.c:727
     ____sys_sendmsg+0x505/0x830 net/socket.c:2566
     ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2620
     __sys_sendmsg net/socket.c:2652 [inline]
     __do_sys_sendmsg net/socket.c:2657 [inline]
     __se_sys_sendmsg net/socket.c:2655 [inline]
     __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2655
     do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
     do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
     entry_SYSCALL_64_after_hwframe+0x77/0x7f



Tested on:

commit:         a5ecfdd9 ipv6: Fix ECMP validation for multipath routes
git tree:       https://github.com/charmitro/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=1151bff4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5a1787205a40c165
dashboard link: https://syzkaller.appspot.com/bug?extid=a259a17220263c2d73fc
compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6

Note: no patches were applied.