[syzbot] [net?] possible deadlock in __netdev_update_features (3)

[syzbot] [net?] possible deadlock in __netdev_update_features (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    b515dc54795e net: ip6_tunnel: use tunnel parameters for fi..
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=149e51b9580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8a830513e9494bd
dashboard link: https://syzkaller.appspot.com/bug?extid=c6c86a1c56b5131f2d97
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/e24d9778837a/disk-b515dc54.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ae4d23043bab/vmlinux-b515dc54.xz
kernel image: https://storage.googleapis.com/syzbot-assets/07018b9230e4/bzImage-b515dc54.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c6c86a1c56b5131f2d97@syzkaller.appspotmail.com

openvswitch: netlink: Tunnel attr 68 out of range max 16
============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz.4.11245/17670 is trying to acquire lock:
ffff88802c0f4e70 (&dev_instance_lock_key#23){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2852 [inline]
ffff88802c0f4e70 (&dev_instance_lock_key#23){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
ffff88802c0f4e70 (&dev_instance_lock_key#23){+.+.}-{4:4}, at: netdev_sync_lower_features net/core/dev.c:10885 [inline]
ffff88802c0f4e70 (&dev_instance_lock_key#23){+.+.}-{4:4}, at: __netdev_update_features+0xd27/0x1ef0 net/core/dev.c:11055

but task is already holding lock:
ffff88802c0f4e70 (&dev_instance_lock_key#23){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2852 [inline]
ffff88802c0f4e70 (&dev_instance_lock_key#23){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
ffff88802c0f4e70 (&dev_instance_lock_key#23){+.+.}-{4:4}, at: __dev_ethtool net/ethtool/ioctl.c:3627 [inline]
ffff88802c0f4e70 (&dev_instance_lock_key#23){+.+.}-{4:4}, at: dev_ethtool+0x47e/0x29c0 net/ethtool/ioctl.c:3669
and the lock comparison function returns 0:

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&dev_instance_lock_key#23);
  lock(&dev_instance_lock_key#23);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by syz.4.11245/17670:
 #0: ffffffff9002d000 (rtnl_mutex){+.+.}-{4:4}, at: __dev_ethtool net/ethtool/ioctl.c:3626 [inline]
 #0: ffffffff9002d000 (rtnl_mutex){+.+.}-{4:4}, at: dev_ethtool+0x3a0/0x29c0 net/ethtool/ioctl.c:3669
 #1: ffff88802c0f4e70 (&dev_instance_lock_key#23){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2852 [inline]
 #1: ffff88802c0f4e70 (&dev_instance_lock_key#23){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
 #1: ffff88802c0f4e70 (&dev_instance_lock_key#23){+.+.}-{4:4}, at: __dev_ethtool net/ethtool/ioctl.c:3627 [inline]
 #1: ffff88802c0f4e70 (&dev_instance_lock_key#23){+.+.}-{4:4}, at: dev_ethtool+0x47e/0x29c0 net/ethtool/ioctl.c:3669

stack backtrace:
CPU: 0 UID: 0 PID: 17670 Comm: syz.4.11245 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_deadlock_bug+0x279/0x290 kernel/locking/lockdep.c:3041
 check_deadlock kernel/locking/lockdep.c:3093 [inline]
 validate_chain kernel/locking/lockdep.c:3895 [inline]
 __lock_acquire+0x24df/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
 netdev_lock include/linux/netdevice.h:2852 [inline]
 netdev_lock_ops include/net/netdev_lock.h:42 [inline]
 netdev_sync_lower_features net/core/dev.c:10885 [inline]
 __netdev_update_features+0xd27/0x1ef0 net/core/dev.c:11055
 netdev_update_features+0x6f/0x100 net/core/dev.c:11112
 macvlan_device_event+0x559/0x880 drivers/net/macvlan.c:1856
 notifier_call_chain+0x1a5/0x3d0 kernel/notifier.c:85
 call_netdevice_notifiers_extack net/core/dev.c:2291 [inline]
 call_netdevice_notifiers net/core/dev.c:2305 [inline]
 netdev_features_change+0x8d/0xd0 net/core/dev.c:1590
 dev_ethtool_locked net/ethtool/ioctl.c:3576 [inline]
 __dev_ethtool net/ethtool/ioctl.c:3634 [inline]
 dev_ethtool+0x1f09/0x29c0 net/ethtool/ioctl.c:3669
 dev_ioctl+0x392/0x1150 net/core/dev_ioctl.c:751
 sock_do_ioctl+0x23e/0x320 net/socket.c:1314
 sock_ioctl+0x57a/0x7e0 net/socket.c:1421
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd7cdd9de99
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fd7ceb8e028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fd7ce026090 RCX: 00007fd7cdd9de99
RDX: 0000200000000080 RSI: 0000000000008946 RDI: 0000000000000009
RBP: 00007fd7cde33eaf R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd7ce026128 R14: 00007fd7ce026090 R15: 00007fffb9a03768
 </TASK>


---
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