[moderation/CI] Re: xsk: Fix circular locking dependency between &net->xdp.lock, &xs->mutex, and netdev_lock_ops

[syzbot ci <syzbot+ci06f7dfaa8255f9ac@syzkaller.appspotmail.com>]

syzbot ci has tested the following series

[v6] xsk: Fix circular locking dependency between &net->xdp.lock, &xs->mutex, and netdev_lock_ops
https://lore.kernel.org/all/20260915081023.7433-1-ahemadkhawar123@gmail.com
* [PATCH bpf-next v6] xsk: Fix circular locking dependency between &net->xdp.lock, &xs->mutex, and netdev_lock_ops

and found the following issue:
possible deadlock in xp_clear_dev

Full report is available here:
https://ci.syzbot.org/series/fd897794-4f0d-45f4-8e63-bcb526e0b175

***

possible deadlock in xp_clear_dev

tree:      bpf-next
URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/bpf/bpf-next.git
base:      b0ca562e0d05cf7afedcfa71c9aed180b72bcc97
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/d5521b86-a0b8-4ffc-ada4-91f534b028bc/config
syz repro: https://ci.syzbot.org/findings/6aa094b3-5f39-460c-b0f7-709bbf72644c/syz_repro

netlink: 14 bytes leftover after parsing attributes in process `syz.1.18'.
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.1.18/5842 is trying to acquire lock:
ffff8881793b4e70 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2861 [inline]
ffff8881793b4e70 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:42 [inline]
ffff8881793b4e70 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: xp_clear_dev+0x13b/0x340 net/xdp/xsk_buff_pool.c:297

but task is already holding lock:
ffff8881bd5ca6b8 (&xs->mutex){+.+.}-{4:4}, at: xsk_notifier+0xcd/0x230 net/xdp/xsk.c:2114

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&xs->mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
       xsk_bind+0x297/0x13f0 net/xdp/xsk.c:1620
       __sys_bind_socket net/socket.c:1945 [inline]
       __sys_bind+0x2e3/0x410 net/socket.c:1976
       __do_sys_bind net/socket.c:1981 [inline]
       __se_sys_bind net/socket.c:1979 [inline]
       __x64_sys_bind+0x7a/0x90 net/socket.c:1979
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&dev_instance_lock_key#3){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3181 [inline]
       check_prevs_add kernel/locking/lockdep.c:3300 [inline]
       validate_chain kernel/locking/lockdep.c:3924 [inline]
       __lock_acquire+0x1520/0x2cf0 kernel/locking/lockdep.c:5253
       lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5886
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
       netdev_lock include/linux/netdevice.h:2861 [inline]
       netdev_lock_ops include/net/netdev_lock.h:42 [inline]
       xp_clear_dev+0x13b/0x340 net/xdp/xsk_buff_pool.c:297
       xsk_notifier+0x1a1/0x230 net/xdp/xsk.c:2123
       notifier_call_chain+0x1a5/0x3d0 kernel/notifier.c:85
       call_netdevice_notifiers_extack net/core/dev.c:2313 [inline]
       call_netdevice_notifiers net/core/dev.c:2327 [inline]
       unregister_netdevice_many_notify+0x17f9/0x2140 net/core/dev.c:12518
       rtnl_delete_link net/core/rtnetlink.c:3652 [inline]
       rtnl_dellink+0x5be/0x810 net/core/rtnetlink.c:3694
       rtnetlink_rcv_msg+0x802/0xc00 net/core/rtnetlink.c:7132
       netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2556
       netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
       netlink_unicast+0x7bd/0x940 net/netlink/af_netlink.c:1345
       netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1900
       sock_sendmsg_nosec+0x13a/0x180 net/socket.c:800
       __sock_sendmsg net/socket.c:815 [inline]
       ____sys_sendmsg+0x54e/0x850 net/socket.c:2713
       ___sys_sendmsg+0x2a5/0x360 net/socket.c:2767
       __sys_sendmsg net/socket.c:2799 [inline]
       __do_sys_sendmsg net/socket.c:2804 [inline]
       __se_sys_sendmsg net/socket.c:2802 [inline]
       __x64_sys_sendmsg+0x1b1/0x290 net/socket.c:2802
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&xs->mutex);
                               lock(&dev_instance_lock_key#3);
                               lock(&xs->mutex);
  lock(&dev_instance_lock_key#3);

 *** DEADLOCK ***

locks held by syz.1.18/5842: 3, last CPU#0:
 #0: ffffffff90036ac0 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock net/core/rtnetlink.c:80 [inline]
 #0: ffffffff90036ac0 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_net_lock include/linux/rtnetlink.h:134 [inline]
 #0: ffffffff90036ac0 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_dellink+0x41b/0x810 net/core/rtnetlink.c:3686
 #1: ffff88810e3ac750 (&net->xdp.lock){+.+.}-{4:4}, at: xsk_notifier+0x89/0x230 net/xdp/xsk.c:2110
 #2: ffff8881bd5ca6b8 (&xs->mutex){+.+.}-{4:4}, at: xsk_notifier+0xcd/0x230 net/xdp/xsk.c:2114

stack backtrace:
CPU: 0 UID: 0 PID: 5842 Comm: syz.1.18 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_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2059
 check_noncircular+0x12e/0x150 kernel/locking/lockdep.c:2191
 check_prev_add kernel/locking/lockdep.c:3181 [inline]
 check_prevs_add kernel/locking/lockdep.c:3300 [inline]
 validate_chain kernel/locking/lockdep.c:3924 [inline]
 __lock_acquire+0x1520/0x2cf0 kernel/locking/lockdep.c:5253
 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5886
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
 netdev_lock include/linux/netdevice.h:2861 [inline]
 netdev_lock_ops include/net/netdev_lock.h:42 [inline]
 xp_clear_dev+0x13b/0x340 net/xdp/xsk_buff_pool.c:297
 xsk_notifier+0x1a1/0x230 net/xdp/xsk.c:2123
 notifier_call_chain+0x1a5/0x3d0 kernel/notifier.c:85
 call_netdevice_notifiers_extack net/core/dev.c:2313 [inline]
 call_netdevice_notifiers net/core/dev.c:2327 [inline]
 unregister_netdevice_many_notify+0x17f9/0x2140 net/core/dev.c:12518
 rtnl_delete_link net/core/rtnetlink.c:3652 [inline]
 rtnl_dellink+0x5be/0x810 net/core/rtnetlink.c:3694
 rtnetlink_rcv_msg+0x802/0xc00 net/core/rtnetlink.c:7132
 netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2556
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x7bd/0x940 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1900
 sock_sendmsg_nosec+0x13a/0x180 net/socket.c:800
 __sock_sendmsg net/socket.c:815 [inline]
 ____sys_sendmsg+0x54e/0x850 net/socket.c:2713
 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2767
 __sys_sendmsg net/socket.c:2799 [inline]
 __do_sys_sendmsg net/socket.c:2804 [inline]
 __se_sys_sendmsg net/socket.c:2802 [inline]
 __x64_sys_sendmsg+0x1b1/0x290 net/socket.c:2802
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f47db99e159
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:00007f47dc90c028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f47dbc25fa0 RCX: 00007f47db99e159
RDX: 0000000004048004 RSI: 00002000000001c0 RDI: 0000000000000005
RBP: 00007f47dba3503b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f47dbc26038 R14: 00007f47dbc25fa0 R15: 00007ffc72db97b8
 </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

---
This report is generated by a bot. It may contain errors.
syzbot ci engineers can be reached at syzkaller@googlegroups.com.

To test a fix for this bug, please reply with `#syz test`
(on a separate line) and attach the patch to the email.

Notes:
- The patch will be applied on top of the tested series (as an
  incremental fix).
- To test a new version of the whole series, please send it directly
  to syzbot@lists.linux.dev.
- Arguments like custom git repos and branches are not supported.

The email will later be sent to:
[ahemadkhawar123@gmail.com ast@kernel.org bpf@vger.kernel.org daniel@iogearbox.net edumazet@google.com hawk@kernel.org horms@kernel.org john.fastabend@gmail.com kuba@kernel.org linux-kernel@vger.kernel.org maciej.fijalkowski@intel.com magnus.karlsson@intel.com netdev@vger.kernel.org pabeni@redhat.com sdf@fomichev.me syzbot@syzkaller.appspotmail.com]

If the report looks fine to you, reply with:
#syz upstream

If the report is a false positive, reply with
#syz invalid