[syzbot] [nfs?] INFO: task hung in nfsd_nl_unlock_filesystem_doit
From: syzbot
Date: Fri Aug 28 2026 - 03:35:48 EST
Hello,
syzbot found the following issue on:
HEAD commit: 45c13f3f9e3b Merge tag 'hwlock-v7.3' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16068d49580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c4f4455f41cf6a92
dashboard link: https://syzkaller.appspot.com/bug?extid=0093d3ab8d8eb2fdde82
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/82d12e132e96/disk-45c13f3f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/46f8d07d4673/vmlinux-45c13f3f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/02439192d277/bzImage-45c13f3f.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0093d3ab8d8eb2fdde82@xxxxxxxxxxxxxxxxxxxxxxxxx
INFO: task syz.2.1768:11730 blocked for more than 143 seconds.
Tainted: G L syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.2.1768 state:D stack:28144 pid:11730 tgid:11729 ppid:5602 task_flags:0x400140 flags:0x00080002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5520 [inline]
__schedule+0x1259/0x6920 kernel/sched/core.c:7270
__schedule_loop kernel/sched/core.c:7347 [inline]
schedule+0xdd/0x2c0 kernel/sched/core.c:7362
schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7419
__mutex_lock_common kernel/locking/mutex.c:726 [inline]
__mutex_lock+0xcbf/0x1bc0 kernel/locking/mutex.c:821
nfsd_nl_unlock_filesystem_doit+0x203/0x410 fs/nfsd/nfsctl.c:2677
genl_family_rcv_msg_doit+0x214/0x300 net/netlink/genetlink.c:1114
genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
genl_rcv_msg+0x560/0x800 net/netlink/genetlink.c:1209
netlink_rcv_skb+0x159/0x420 net/netlink/af_netlink.c:2556
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
netlink_unicast+0x585/0x850 net/netlink/af_netlink.c:1345
netlink_sendmsg+0x8b0/0xda0 net/netlink/af_netlink.c:1900
sock_sendmsg_nosec net/socket.c:800 [inline]
__sock_sendmsg net/socket.c:815 [inline]
____sys_sendmsg+0xa4d/0xbe0 net/socket.c:2713
___sys_sendmsg+0x190/0x1e0 net/socket.c:2767
__sys_sendmsg+0x160/0x210 net/socket.c:2799
do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f88cbb9e0d9
RSP: 002b:00007f88cca9f028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f88cbe25fa0 RCX: 00007f88cbb9e0d9
RDX: 0000000004000080 RSI: 0000200000000100 RDI: 0000000000000003
RBP: 00007f88cbc35024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f88cbe26038 R14: 00007f88cbe25fa0 R15: 00007ffd44e926f8
</TASK>
Showing all locks held in the system:
locks held by khungtaskd/32: 1, last CPU#0:
#0: ffffffff8edec060 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:309 [inline]
#0: ffffffff8edec060 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
#0: ffffffff8edec060 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x3d/0x184 kernel/locking/lockdep.c:6793
locks held by udevd/4965: 1, on CPU#0:
#0: ffff88801d2bf180 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_dop_revalidate+0xa5/0x7e0 fs/kernfs/dir.c:1217
locks held by getty/5352: 2, on CPU#1:
#0: ffff8880380ee0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x24/0x80 drivers/tty/tty_ldisc.c:243
#1: ffffc9000322b2e8 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x419/0x14e0 drivers/tty/n_tty.c:2211
locks held by kworker/0:6/5706: 3, on CPU#0:
#0: ffff88801c057140 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x1466/0x1b10 kernel/workqueue.c:3362
#1: ffffc90004c37d08 (deferred_process_work){+.+.}-{0:0}, at: process_one_work+0xa2c/0x1b10 kernel/workqueue.c:3363
#2: ffffffff90cc9840 (rtnl_mutex){+.+.}-{4:4}, at: switchdev_deferred_process_work+0xe/0x20 net/switchdev/switchdev.c:104
locks held by syz.0.1424/10896: 2, on CPU#0:
#0: ffffffff90d78be8 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1217
#1: ffffffff8f284440 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_nl_listener_set_doit+0x1a3/0x1dc0 fs/nfsd/nfsctl.c:2057
locks held by syz.2.1768/11730: 2, on CPU#1:
#0: ffffffff90d78be8 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1217
#1: ffffffff8f284440 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_nl_unlock_filesystem_doit+0x203/0x410 fs/nfsd/nfsctl.c:2677
locks held by syz.1.2261/12930: 2, on CPU#1:
#0: ffff888055b400e8 (&type->s_umount_key#75){+.+.}-{4:4}, at: __super_lock fs/super.c:60 [inline]
#0: ffff888055b400e8 (&type->s_umount_key#75){+.+.}-{4:4}, at: __super_lock_excl fs/super.c:75 [inline]
#0: ffff888055b400e8 (&type->s_umount_key#75){+.+.}-{4:4}, at: deactivate_super fs/super.c:631 [inline]
#0: ffff888055b400e8 (&type->s_umount_key#75){+.+.}-{4:4}, at: deactivate_super+0xe2/0x110 fs/super.c:628
#1: ffffffff8f284440 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:582
locks held by syz-executor/13344: 1, last CPU#0:
#0: ffffffff8ef90080 (pcpu_alloc_mutex){+.+.}-{4:4}, at: pcpu_alloc_noprof+0xfa8/0x1e50 mm/percpu.c:1796
locks held by syz.5.3369/16148: 4, last CPU#0:
#0: ffff88804d75d1b0 (&tty->legacy_mutex){+.+.}-{4:4}, at: tty_init_dev.part.0+0x39/0x470 drivers/tty/tty_io.c:1379
#1: ffff888031c242a8 (&port->mutex){+.+.}-{4:4}, at: class_mutex_constructor include/linux/mutex.h:253 [inline]
#1: ffff888031c242a8 (&port->mutex){+.+.}-{4:4}, at: tty_port_open+0x8e/0x1f0 drivers/tty/tty_port.c:764
#2: ffff888027933d18 (&serial->disc_mutex){+.+.}-{4:4}, at: serial_port_activate+0x52/0x290 drivers/usb/serial/usb-serial.c:258
#3: ffff8880887f8460 (&tdev->td_open_close_lock){+.+.}-{4:4}, at: ti_open+0xb4/0xce0 drivers/usb/serial/ti_usb_3410_5052.c:653
locks held by syz.3.3374/16166: 4, last CPU#0:
#0: ffffffff90c998a0 (br_ioctl_mutex){+.+.}-{4:4}, at: br_ioctl_call+0x34/0xa0 net/socket.c:1296
#1: ffffffff90cc9840 (rtnl_mutex){+.+.}-{4:4}, at: br_ioctl_stub+0x2af/0x4d0 net/bridge/br_ioctl.c:418
#2: ffff88801d2bf180 (&root->kernfs_rwsem){++++}-{4:4}, at: kernfs_add_one+0x38/0xaa0 fs/kernfs/dir.c:825
#3: ffff88801d2bf210 (&root->kernfs_iattr_rwsem){++++}-{4:4}, at: kernfs_link_sibling+0x555/0x850 fs/kernfs/dir.c:411
locks held by syz.6.3376/16171: 1, last CPU#0:
#0: ffff88802cf9f470 (&u->iolock){+.+.}-{4:4}, at: __unix_dgram_recvmsg+0x255/0xc30 net/unix/af_unix.c:2587
=============================================
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 32 Comm: khungtaskd Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
nmi_cpu_backtrace.cold+0x12d/0x151 lib/nmi_backtrace.c:123
nmi_trigger_cpumask_backtrace+0x21f/0x2a0 lib/nmi_backtrace.c:66
trigger_all_cpu_backtrace include/linux/nmi.h:164 [inline]
__sys_info lib/sys_info.c:157 [inline]
sys_info+0x141/0x190 lib/sys_info.c:165
check_hung_uninterruptible_tasks kernel/hung_task.c:353 [inline]
watchdog+0xcb1/0x1030 kernel/hung_task.c:561
kthread+0x373/0x450 kernel/kthread.c:436
ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
---
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