Subject: [syzbot] [kernfs?] possible deadlock in __kernfs_remove (3)

From: syzbot <[email-masked]>
Date: Wed, 25 Feb 2026 22:07:24 -0800

Hello,

syzbot found the following issue on:

HEAD commit:    d4f687fbbce4 ovpn: tcp - fix packet extraction from stream
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=12dba44a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=665cbf0979cda6c5
dashboard link: https://syzkaller.appspot.com/bug?extid=1075f6dc93f398c1857e
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ee42a61b2ee7/disk-d4f687fb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e5470ff18ff8/vmlinux-d4f687fb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d50957aaabf2/bzImage-d4f687fb.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.2.13134/20856 is trying to acquire lock:
ffff888064e8e3c8 (kn->active#14){++++}-{0:0}, at: __kernfs_remove+0x3cf/0x660 fs/kernfs/dir.c:1513

but task is already holding lock:
ffff888033048788 (&rdev->wiphy.mtx){+.+.}-{4:4}, at: class_wiphy_constructor include/net/cfg80211.h:6441 [inline]
ffff888033048788 (&rdev->wiphy.mtx){+.+.}-{4:4}, at: ieee80211_remove_interfaces+0x132/0x6d0 net/mac80211/iface.c:2415

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #2 (&rdev->wiphy.mtx){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:614 [inline]
       __mutex_lock+0x19f/0x1300 kernel/locking/mutex.c:776
       class_wiphy_constructor include/net/cfg80211.h:6441 [inline]
       ieee80211_change_mac+0xb5/0x1410 net/mac80211/iface.c:324
       netif_set_mac_address+0x317/0x4e0 net/core/dev.c:9989
       do_setlink+0x9b1/0x4590 net/core/rtnetlink.c:3110
       rtnl_changelink net/core/rtnetlink.c:3776 [inline]
       __rtnl_newlink net/core/rtnetlink.c:3935 [inline]
       rtnl_newlink+0x15a9/0x1be0 net/core/rtnetlink.c:4072
       rtnetlink_rcv_msg+0x7d5/0xbe0 net/core/rtnetlink.c:6958
       netlink_rcv_skb+0x232/0x4b0 net/netlink/af_netlink.c:2550
       netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
       netlink_unicast+0x80f/0x9b0 net/netlink/af_netlink.c:1344
       netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1894
       sock_sendmsg_nosec net/socket.c:727 [inline]
       __sock_sendmsg net/socket.c:742 [inline]
       ____sys_sendmsg+0xa68/0xad0 net/socket.c:2592
       ___sys_sendmsg+0x2a5/0x360 net/socket.c:2646
       __sys_sendmsg net/socket.c:2678 [inline]
       __do_sys_sendmsg net/socket.c:2683 [inline]
       __se_sys_sendmsg net/socket.c:2681 [inline]
       __x64_sys_sendmsg+0x1bd/0x2a0 net/socket.c:2681
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (dev_addr_sem){++++}-{4:4}:
       down_read+0x47/0x2e0 kernel/locking/rwsem.c:1537
       address_show+0x25/0x250 net/core/net-sysfs.c:266
       dev_attr_show+0x58/0xc0 drivers/base/core.c:2421
       sysfs_kf_seq_show+0x310/0x490 fs/sysfs/file.c:65
       seq_read_iter+0x4ef/0xe10 fs/seq_file.c:231
       new_sync_read fs/read_write.c:493 [inline]
       vfs_read+0x582/0xa70 fs/read_write.c:574
       ksys_read+0x150/0x270 fs/read_write.c:717
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (kn->active#14){++++}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
       lock_acquire+0xf0/0x2e0 kernel/locking/lockdep.c:5868
       kernfs_drain+0x284/0x600 fs/kernfs/dir.c:511
       __kernfs_remove+0x3cf/0x660 fs/kernfs/dir.c:1513
       kernfs_remove_by_name_ns+0xaf/0x130 fs/kernfs/dir.c:1722
       kernfs_remove_by_name include/linux/kernfs.h:633 [inline]
       remove_files fs/sysfs/group.c:28 [inline]
       sysfs_remove_group+0xfc/0x2e0 fs/sysfs/group.c:328
       sysfs_remove_groups+0x54/0xb0 fs/sysfs/group.c:352
       device_remove_groups drivers/base/core.c:2843 [inline]
       device_remove_attrs+0x229/0x280 drivers/base/core.c:2979
       device_del+0x51f/0x8f0 drivers/base/core.c:3877
       unregister_netdevice_many_notify+0x1e0e/0x2370 net/core/dev.c:12438
       unregister_netdevice_many net/core/dev.c:12466 [inline]
       unregister_netdevice_queue+0x31f/0x360 net/core/dev.c:12280
       unregister_netdevice include/linux/netdevice.h:3408 [inline]
       _cfg80211_unregister_wdev+0x155/0x570 net/wireless/core.c:1297
       ieee80211_remove_interfaces+0x49c/0x6d0 net/mac80211/iface.c:2440
       ieee80211_unregister_hw+0x5d/0x2c0 net/mac80211/main.c:1691
       mac80211_hwsim_del_radio+0x28a/0x490 drivers/net/wireless/virtual/mac80211_hwsim.c:5916
       remove_user_radios drivers/net/wireless/virtual/mac80211_hwsim.c:6727 [inline]
       mac80211_hwsim_netlink_notify+0xfae/0x1310 drivers/net/wireless/virtual/mac80211_hwsim.c:6741
       notifier_call_chain+0x1be/0x400 kernel/notifier.c:85
       blocking_notifier_call_chain+0x6a/0x90 kernel/notifier.c:380
       netlink_release+0x123b/0x1ad0 net/netlink/af_netlink.c:761
       __sock_release net/socket.c:662 [inline]
       sock_close+0xc3/0x240 net/socket.c:1455
       __fput+0x44f/0xa70 fs/file_table.c:469
       task_work_run+0x1d9/0x270 kernel/task_work.c:233
       resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
       __exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
       exit_to_user_mode_loop+0xed/0x480 kernel/entry/common.c:98
       __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
       syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
       syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline]
       do_syscall_64+0x32d/0xf80 arch/x86/entry/syscall_64.c:100
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  kn->active#14 --> dev_addr_sem --> &rdev->wiphy.mtx

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&rdev->wiphy.mtx);
                               lock(dev_addr_sem);
                               lock(&rdev->wiphy.mtx);
  lock(kn->active#14);

 *** DEADLOCK ***

4 locks held by syz.2.13134/20856:
 #0: ffff88809099c708 (&sb->s_type->i_mutex_key#14){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:1028 [inline]
 #0: ffff88809099c708 (&sb->s_type->i_mutex_key#14){+.+.}-{4:4}, at: __sock_release net/socket.c:661 [inline]
 #0: ffff88809099c708 (&sb->s_type->i_mutex_key#14){+.+.}-{4:4}, at: sock_close+0x9b/0x240 net/socket.c:1455
 #1: ffffffff8fc374b0 ((netlink_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain+0x54/0x90 kernel/notifier.c:379
 #2: ffffffff8fbcb808 (rtnl_mutex){+.+.}-{4:4}, at: ieee80211_unregister_hw+0x55/0x2c0 net/mac80211/main.c:1684
 #3: ffff888033048788 (&rdev->wiphy.mtx){+.+.}-{4:4}, at: class_wiphy_constructor include/net/cfg80211.h:6441 [inline]
 #3: ffff888033048788 (&rdev->wiphy.mtx){+.+.}-{4:4}, at: ieee80211_remove_interfaces+0x132/0x6d0 net/mac80211/iface.c:2415

stack backtrace:
CPU: 0 UID: 0 PID: 20856 Comm: syz.2.13134 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2043
 check_noncircular+0x12e/0x150 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3165 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0xf0/0x2e0 kernel/locking/lockdep.c:5868
 kernfs_drain+0x284/0x600 fs/kernfs/dir.c:511
 __kernfs_remove+0x3cf/0x660 fs/kernfs/dir.c:1513
 kernfs_remove_by_name_ns+0xaf/0x130 fs/kernfs/dir.c:1722
 kernfs_remove_by_name include/linux/kernfs.h:633 [inline]
 remove_files fs/sysfs/group.c:28 [inline]
 sysfs_remove_group+0xfc/0x2e0 fs/sysfs/group.c:328
 sysfs_remove_groups+0x54/0xb0 fs/sysfs/group.c:352
 device_remove_groups drivers/base/core.c:2843 [inline]
 device_remove_attrs+0x229/0x280 drivers/base/core.c:2979
 device_del+0x51f/0x8f0 drivers/base/core.c:3877
 unregister_netdevice_many_notify+0x1e0e/0x2370 net/core/dev.c:12438
 unregister_netdevice_many net/core/dev.c:12466 [inline]
 unregister_netdevice_queue+0x31f/0x360 net/core/dev.c:12280
 unregister_netdevice include/linux/netdevice.h:3408 [inline]
 _cfg80211_unregister_wdev+0x155/0x570 net/wireless/core.c:1297
 ieee80211_remove_interfaces+0x49c/0x6d0 net/mac80211/iface.c:2440
 ieee80211_unregister_hw+0x5d/0x2c0 net/mac80211/main.c:1691
 mac80211_hwsim_del_radio+0x28a/0x490 drivers/net/wireless/virtual/mac80211_hwsim.c:5916
 remove_user_radios drivers/net/wireless/virtual/mac80211_hwsim.c:6727 [inline]
 mac80211_hwsim_netlink_notify+0xfae/0x1310 drivers/net/wireless/virtual/mac80211_hwsim.c:6741
 notifier_call_chain+0x1be/0x400 kernel/notifier.c:85
 blocking_notifier_call_chain+0x6a/0x90 kernel/notifier.c:380
 netlink_release+0x123b/0x1ad0 net/netlink/af_netlink.c:761
 __sock_release net/socket.c:662 [inline]
 sock_close+0xc3/0x240 net/socket.c:1455
 __fput+0x44f/0xa70 fs/file_table.c:469
 task_work_run+0x1d9/0x270 kernel/task_work.c:233
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 __exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
 exit_to_user_mode_loop+0xed/0x480 kernel/entry/common.c:98
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline]
 do_syscall_64+0x32d/0xf80 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f182d99c629
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:00007f182e8af028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: 0000000000000018 RBX: 00007f182dc15fa0 RCX: 00007f182d99c629
RDX: 0000000000000300 RSI: 0000200000000040 RDI: 0000000000000004
RBP: 00007f182da32b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f182dc16038 R14: 00007f182dc15fa0 R15: 00007fff4353ce78
 </TASK>

---
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