[syzbot] [net?] possible deadlock in __netdev_update_features (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 6146a0f1dfae Linux 6.18-rc4
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17b18012580000
kernel config: https://syzkaller.appspot.com/x/.config?x=e46b8a1c645465a9
dashboard link: https://syzkaller.appspot.com/bug?extid=f900128d760321f31225
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c84c238d0311/disk-6146a0f1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9ce2b6a4b897/vmlinux-6146a0f1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3e9c6bea4a10/bzImage-6146a0f1.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f90012...@syzkaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz.1.3525/19446 is trying to acquire lock:
ffff888070d30d38 (&dev_instance_lock_key#20){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2765 [inline]
ffff888070d30d38 (&dev_instance_lock_key#20){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
ffff888070d30d38 (&dev_instance_lock_key#20){+.+.}-{4:4}, at: netdev_sync_lower_features net/core/dev.c:10737 [inline]
ffff888070d30d38 (&dev_instance_lock_key#20){+.+.}-{4:4}, at: __netdev_update_features+0xcb1/0x1be0 net/core/dev.c:10907

but task is already holding lock:
ffff888070d30d38 (&dev_instance_lock_key#20){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2765 [inline]
ffff888070d30d38 (&dev_instance_lock_key#20){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
ffff888070d30d38 (&dev_instance_lock_key#20){+.+.}-{4:4}, at: __dev_ethtool net/ethtool/ioctl.c:3285 [inline]
ffff888070d30d38 (&dev_instance_lock_key#20){+.+.}-{4:4}, at: dev_ethtool+0x716/0x19c0 net/ethtool/ioctl.c:3554
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#20);
lock(&dev_instance_lock_key#20);

*** DEADLOCK ***

May be due to missing lock nesting notation

2 locks held by syz.1.3525/19446:
#0: ffffffff8f2cb648 (rtnl_mutex){+.+.}-{4:4}, at: dev_ethtool+0x1d0/0x19c0 net/ethtool/ioctl.c:3553
#1: ffff888070d30d38 (&dev_instance_lock_key#20){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2765 [inline]
#1: ffff888070d30d38 (&dev_instance_lock_key#20){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
#1: ffff888070d30d38 (&dev_instance_lock_key#20){+.+.}-{4:4}, at: __dev_ethtool net/ethtool/ioctl.c:3285 [inline]
#1: ffff888070d30d38 (&dev_instance_lock_key#20){+.+.}-{4:4}, at: dev_ethtool+0x716/0x19c0 net/ethtool/ioctl.c:3554

stack backtrace:
CPU: 0 UID: 0 PID: 19446 Comm: syz.1.3525 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_deadlock_bug+0x28b/0x2a0 kernel/locking/lockdep.c:3041
check_deadlock kernel/locking/lockdep.c:3093 [inline]
validate_chain+0x1a3f/0x2140 kernel/locking/lockdep.c:3895
__lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
__mutex_lock_common kernel/locking/mutex.c:598 [inline]
__mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760
netdev_lock include/linux/netdevice.h:2765 [inline]
netdev_lock_ops include/net/netdev_lock.h:42 [inline]
netdev_sync_lower_features net/core/dev.c:10737 [inline]
__netdev_update_features+0xcb1/0x1be0 net/core/dev.c:10907
netdev_change_features+0x72/0xd0 net/core/dev.c:10981
bond_compute_features+0x615/0x680 drivers/net/bonding/bond_main.c:1559
bond_slave_netdev_event drivers/net/bonding/bond_main.c:4030 [inline]
bond_netdev_event+0x72e/0xe80 drivers/net/bonding/bond_main.c:4075
notifier_call_chain+0x1b6/0x3e0 kernel/notifier.c:85
call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
call_netdevice_notifiers net/core/dev.c:2281 [inline]
netdev_features_change+0x85/0xc0 net/core/dev.c:1570
__dev_ethtool net/ethtool/ioctl.c:3521 [inline]
dev_ethtool+0x1541/0x19c0 net/ethtool/ioctl.c:3554
dev_ioctl+0x392/0x1150 net/core/dev_ioctl.c:773
sock_do_ioctl+0x22c/0x300 net/socket.c:1268
sock_ioctl+0x576/0x790 net/socket.c:1375
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+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc1a3f8efc9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fc1a4e6f038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fc1a41e5fa0 RCX: 00007fc1a3f8efc9
RDX: 0000200000000000 RSI: 0000000000008946 RDI: 0000000000000004
RBP: 00007fc1a4011f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc1a41e6038 R14: 00007fc1a41e5fa0 R15: 00007fc1a430fa28
</TASK>


---
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