Re: [moderation/CI] Re: net: ethtool: let ops locked drivers run without rtnl_lock

#syz upstream

On Fri, May 29, 2026 at 9:37 AM syzbot ci
<[email protected]> wrote:
>
> syzbot ci has tested the following series
>
> [v1] net: ethtool: let ops locked drivers run without rtnl_lock
> https://lore.kernel.org/all/[email protected]
> * [PATCH net-next 01/14] net: ethtool: cmis_cdb: hold instance lock for ops locked devices
> * [PATCH net-next 02/14] net: ethtool: make sure __ethtool_get_link_ksettings() is ops-locked
> * [PATCH net-next 03/14] net: ethtool: serialize broadcast notification sequence allocation
> * [PATCH net-next 04/14] net: ethtool: relax ethnl_req_get_phydev() locking assertion
> * [PATCH net-next 05/14] net: ethtool: make dev->hwprov ops-protected
> * [PATCH net-next 06/14] net: ethtool: optionally skip rtnl_lock on Netlink path for GET ops
> * [PATCH net-next 07/14] net: ethtool: optionally skip rtnl_lock on Netlink path for SET ops
> * [PATCH net-next 08/14] net: ethtool: optionally skip rtnl_lock in cable test handlers
> * [PATCH net-next 09/14] net: ethtool: optionally skip rtnl_lock in ethnl_tsinfo_dumpit()
> * [PATCH net-next 10/14] net: ethtool: optionally skip rtnl_lock in ethnl_act_module_fw_flash()
> * [PATCH net-next 11/14] net: ethtool: optionally skip rtnl_lock in RSS context handlers
> * [PATCH net-next 12/14] net: ethtool: ioctl: concentrate the locking
> * [PATCH net-next 13/14] net: ethtool: optionally skip rtnl_lock on IOCTL path
> * [PATCH net-next 14/14] docs: net: ethtool: document ops-locked drivers and op_needs_rtnl
>
> and found the following issue:
> possible deadlock in __ethtool_get_link_ksettings
>
> Full report is available here:
> https://ci.syzbot.org/series/ada8852f-9efd-4b85-87aa-2f5d8fe16040
>
> ***
>
> possible deadlock in __ethtool_get_link_ksettings
>
> tree:      net-next
> URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/netdev/net-next.git
> base:      9a82e387e27a4422a0d2d9d644180b7bd913e85a
> arch:      amd64
> compiler:  Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
> config:    https://ci.syzbot.org/builds/2968208d-6483-4d38-be45-de68d3b94775/config
> syz repro: https://ci.syzbot.org/findings/d8670aa1-9241-49be-8108-cdbed56dd4a5/syz_repro
>
> dummy0: entered promiscuous mode
> bridge0: port 3(dummy0) entered blocking state
> bridge0: port 3(dummy0) entered forwarding state
> ============================================
> WARNING: possible recursive locking detected
> syzkaller #0 Not tainted
> --------------------------------------------
> syz.1.28/5852 is trying to acquire lock:
> ffff888115f78dc8 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2833 [inline]
> ffff888115f78dc8 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
> ffff888115f78dc8 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: __ethtool_get_link_ksettings+0x12b/0x290 net/ethtool/ioctl.c:462
>
> but task is already holding lock:
> ffff888115f78dc8 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2833 [inline]
> ffff888115f78dc8 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
> ffff888115f78dc8 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: do_setlink+0x3d2/0x45a0 net/core/rtnetlink.c:3117
> 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#3);
>   lock(&dev_instance_lock_key#3);
>
>  *** DEADLOCK ***
>
>  May be due to missing lock nesting notation
>
> 2 locks held by syz.1.28/5852:
>  #0: ffffffff8fdd2d80 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock net/core/rtnetlink.c:80 [inline]
>  #0: ffffffff8fdd2d80 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_nets_lock net/core/rtnetlink.c:341 [inline]
>  #0: ffffffff8fdd2d80 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_setlink+0x6bb/0xb40 net/core/rtnetlink.c:3527
>  #1: ffff888115f78dc8 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2833 [inline]
>  #1: ffff888115f78dc8 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
>  #1: ffff888115f78dc8 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: do_setlink+0x3d2/0x45a0 net/core/rtnetlink.c:3117
>
> stack backtrace:
> CPU: 0 UID: 0 PID: 5852 Comm: syz.1.28 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
> 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+0x253f/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+0x1a3/0x1550 kernel/locking/mutex.c:820
>  netdev_lock include/linux/netdevice.h:2833 [inline]
>  netdev_lock_ops include/net/netdev_lock.h:42 [inline]
>  __ethtool_get_link_ksettings+0x12b/0x290 net/ethtool/ioctl.c:462
>  port_cost+0xc0/0x3a0 net/bridge/br_if.c:39
>  br_port_carrier_check+0x12d/0x3f0 net/bridge/br_if.c:80
>  br_device_event+0x65c/0x970 net/bridge/br.c:101
>  notifier_call_chain+0x1ad/0x3d0 kernel/notifier.c:85
>  __dev_notify_flags+0x248/0x310 net/core/dev.c:9804
>  netif_change_flags+0xe8/0x1a0 net/core/dev.c:9819
>  do_setlink+0xfa5/0x45a0 net/core/rtnetlink.c:3207
>  rtnl_setlink+0x792/0xb40 net/core/rtnetlink.c:3537
>  rtnetlink_rcv_msg+0x7d5/0xbe0 net/core/rtnetlink.c:7062
>  netlink_rcv_skb+0x232/0x4b0 net/netlink/af_netlink.c:2556
>  netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
>  netlink_unicast+0x75c/0x8e0 net/netlink/af_netlink.c:1345
>  netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1900
>  sock_sendmsg_nosec net/socket.c:787 [inline]
>  __sock_sendmsg net/socket.c:802 [inline]
>  ____sys_sendmsg+0x972/0x9f0 net/socket.c:2698
>  ___sys_sendmsg+0x2a5/0x360 net/socket.c:2752
>  __sys_sendmsg net/socket.c:2784 [inline]
>  __do_sys_sendmsg net/socket.c:2789 [inline]
>  __se_sys_sendmsg net/socket.c:2787 [inline]
>  __x64_sys_sendmsg+0x1bd/0x2a0 net/socket.c:2787
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0x15f/0x560 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f087ad9ce59
> 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:00007f087bc25028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
> RAX: ffffffffffffffda RBX: 00007f087b015fa0 RCX: 00007f087ad9ce59
> RDX: 0000000000000000 RSI: 0000200000000040 RDI: 0000000000000004
> RBP: 00007f087ae32d6f R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f087b016038 R14: 00007f087b015fa0 R15: 00007ffcefdf0348
>  </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: [email protected]
>
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