[syzbot ci] Re: net: opt loopback into instance locking

[syzbot ci <syzbot+ci721ed44e87a0b71e@syzkaller.appspotmail.com>]

syzbot ci has tested the following series

[v1] net: opt loopback into instance locking
https://lore.kernel.org/all/20260918210419.4088201-1-kuba@kernel.org
* [PATCH net-next] net: opt loopback into instance locking

and found the following issue:
WARNING in ipv6_add_dev

Full report is available here:
https://ci.syzbot.org/series/f12bc892-cfa6-4277-beac-794482c9a3f7

***

WARNING in ipv6_add_dev

tree:      net-next
URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/netdev/net-next.git
base:      8830e65ed46de41f849eefb8ba227d4852c460f6
arch:      amd64
compiler:  Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
config:    https://ci.syzbot.org/builds/ae142b5c-beb2-4c41-814c-2cd3e14bdbb0/config

usbcore: registered new interface driver snd-usb-hiface
usbcore: registered new interface driver snd-bcd2000
usbcore: registered new interface driver snd_usb_pod
usbcore: registered new interface driver snd_usb_podhd
usbcore: registered new interface driver snd_usb_toneport
usbcore: registered new interface driver snd_usb_variax
drop_monitor: Initializing network drop monitor service
NET: Registered PF_LLC protocol family
GACT probability on
Mirror/redirect action on
Simple TC action Loaded
u32 classifier
    Performance counters on
    input device check on
    Actions configured
nf_conntrack_irc: The irc conntrack helper is scheduled for removal.
Please contact the netfilter-devel mailing list if you still need this.
The pptp conntrack helper is scheduled for removal.
Please contact the netfilter-devel mailing list if you still need this.
The DCCP match is deprecated and scheduled to be removed in 2027.
Please contact the netfilter-devel mailing list or update your iptables rules
xt_time: kernel timezone is -0000
IPVS: Registered protocols (TCP, UDP, SCTP, AH, ESP)
IPVS: Connection hash table configured (size=4096, memory=32Kbytes)
IPVS: ipvs loaded.
IPVS: [rr] scheduler registered.
IPVS: [wrr] scheduler registered.
IPVS: [lc] scheduler registered.
IPVS: [wlc] scheduler registered.
IPVS: [fo] scheduler registered.
IPVS: [ovf] scheduler registered.
IPVS: [lblc] scheduler registered.
IPVS: [lblcr] scheduler registered.
IPVS: [dh] scheduler registered.
IPVS: [sh] scheduler registered.
IPVS: [mh] scheduler registered.
IPVS: [sed] scheduler registered.
IPVS: [nq] scheduler registered.
IPVS: [twos] scheduler registered.
IPVS: [sip] pe registered.
ipip: IPv4 and MPLS over IPv4 tunneling driver
gre: GRE over IPv4 demultiplexer driver
ip_gre: GRE over IPv4 tunneling driver
IPv4 over IPsec tunneling driver
Initializing XFRM netlink socket
IPsec XFRM device driver
xfrm_iptfs: IPsec IP-TFS tunnel mode module
NET: Registered PF_INET6 protocol family
------------[ cut here ]------------
debug_locks && !(lock_is_held(&(&dev->lock)->dep_map) != 0)
WARNING: ./include/net/netdev_lock.h:70 at ipv6_add_dev+0xfc1/0x1400, CPU#0: swapper/0/1
Modules linked in:
CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:ipv6_add_dev+0xfc1/0x1400
Code: ff ff e8 a2 6e 3a f7 48 8d 3d 6b 56 fd 05 48 c7 c6 80 a2 32 8d ba 80 01 00 00 67 48 0f b9 3a e9 ab f0 ff ff e8 80 6e 3a f7 90 <0f> 0b 90 e9 cb f1 ff ff e8 72 6e 3a f7 48 8d 3d 5b 56 fd 05 48 c7
RSP: 0000:ffffc900000678c0 EFLAGS: 00010293
RAX: ffffffff8a8d6400 RBX: dffffc0000000000 RCX: ffff888102abda00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffffff90253707 R09: 1ffffffff204a6e0
R10: dffffc0000000000 R11: fffffbfff204a6e1 R12: dffffc0000000000
R13: ffff88810c036000 R14: ffffffff8caa6a10 R15: ffff88810c036008
FS:  0000000000000000(0000) GS:ffff88818d6cd000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff88823ffff000 CR3: 000000000eb48000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 addrconf_init+0x8b/0x170
 inet6_init+0x228/0x3f0
 do_one_initcall+0x250/0x870
 do_initcall_level+0x10a/0x1a0
 do_initcalls+0x59/0xa0
 kernel_init_freeable+0x29d/0x3e0
 kernel_init+0x22/0x1d0
 ret_from_fork+0x514/0xb70
 ret_from_fork_asm+0x1a/0x30
 </TASK>


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
  Tested-by: syzbot@syzkaller.appspotmail.com

---
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