Message-Id: <4bc8b687-382b-4243-b5ab-48f83d87f6c5@app.fastmail.com>
Date: Wed, 03 Dec 2025 10:56:36 -0500
From: "Chuck Lever" <cel@...nel.org>
To: syzbot <syzbot+31dce4175fcaed9dae98@...kaller.appspotmail.com>,
 "Dai Ngo" <Dai.Ngo@...cle.com>, "Chuck Lever" <chuck.lever@...cle.com>,
 "Jeff Layton" <jlayton@...nel.org>, linux-kernel@...r.kernel.org,
 linux-nfs@...r.kernel.org, NeilBrown <neil@...wn.name>,
 "Olga Kornievskaia" <okorniev@...hat.com>, syzkaller-bugs@...glegroups.com,
 "Tom Talpey" <tom@...pey.com>
Subject: Re: [syzbot] [nfs?] INFO: task hung in nfsd_nl_version_set_doit (2)



On Mon, Dec 1, 2025, at 5:38 PM, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    7d0a66e4bb90 Linux 6.18
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=13d52512580000
> kernel config:  
> https://syzkaller.appspot.com/x/.config?x=1cd7f786c0f5182f
> dashboard link: 
> https://syzkaller.appspot.com/bug?extid=31dce4175fcaed9dae98
> compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU 
> Binutils for Debian) 2.40
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image: 
> https://storage.googleapis.com/syzbot-assets/426e88dc4200/disk-7d0a66e4.raw.xz
> vmlinux: 
> https://storage.googleapis.com/syzbot-assets/07f64a43f087/vmlinux-7d0a66e4.xz
> kernel image: 
> https://storage.googleapis.com/syzbot-assets/43778a8316e2/bzImage-7d0a66e4.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+31dce4175fcaed9dae98@...kaller.appspotmail.com
>
> INFO: task syz.7.3138:20679 blocked for more than 143 seconds.
>       Tainted: G          I         syzkaller #0
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this 
> message.
> task:syz.7.3138      state:D stack:27528 pid:20679 tgid:20678 
> ppid:19956  task_flags:0x400140 flags:0x00080002
> Call Trace:
>  <TASK>
>  context_switch kernel/sched/core.c:5325 [inline]
>  __schedule+0x1190/0x5de0 kernel/sched/core.c:6929
>  __schedule_loop kernel/sched/core.c:7011 [inline]
>  schedule+0xe7/0x3a0 kernel/sched/core.c:7026
>  schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7083
>  __mutex_lock_common kernel/locking/mutex.c:676 [inline]
>  __mutex_lock+0x818/0x1060 kernel/locking/mutex.c:760
>  nfsd_nl_version_set_doit+0xc4/0x7a0 fs/nfsd/nfsctl.c:1730
>  genl_family_rcv_msg_doit+0x209/0x2f0 net/netlink/genetlink.c:1115
>  genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
>  genl_rcv_msg+0x55c/0x800 net/netlink/genetlink.c:1210
>  netlink_rcv_skb+0x158/0x420 net/netlink/af_netlink.c:2552
>  genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
>  netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
>  netlink_unicast+0x5aa/0x870 net/netlink/af_netlink.c:1346
>  netlink_sendmsg+0x8c8/0xdd0 net/netlink/af_netlink.c:1896
>  sock_sendmsg_nosec net/socket.c:727 [inline]
>  __sock_sendmsg net/socket.c:742 [inline]
>  ____sys_sendmsg+0xa98/0xc70 net/socket.c:2630
>  ___sys_sendmsg+0x134/0x1d0 net/socket.c:2684
>  __sys_sendmsg+0x16d/0x220 net/socket.c:2716
>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>  do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7ff6b358f7c9
> RSP: 002b:00007ff6b43f7038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
> RAX: ffffffffffffffda RBX: 00007ff6b37e5fa0 RCX: 00007ff6b358f7c9
> RDX: 0000000004004000 RSI: 0000200000003200 RDI: 0000000000000003
> RBP: 00007ff6b3613f91 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007ff6b37e6038 R14: 00007ff6b37e5fa0 R15: 00007fffed6dad48
>  </TASK>
> INFO: task syz.6.3144:20706 blocked for more than 147 seconds.
>       Tainted: G          I         syzkaller #0
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this 
> message.
> task:syz.6.3144      state:D stack:27448 pid:20706 tgid:20705 
> ppid:19445  task_flags:0x400140 flags:0x00080002
> Call Trace:
>  <TASK>
>  context_switch kernel/sched/core.c:5325 [inline]
>  __schedule+0x1190/0x5de0 kernel/sched/core.c:6929
>  __schedule_loop kernel/sched/core.c:7011 [inline]
>  schedule+0xe7/0x3a0 kernel/sched/core.c:7026
>  schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7083
>  __mutex_lock_common kernel/locking/mutex.c:676 [inline]
>  __mutex_lock+0x818/0x1060 kernel/locking/mutex.c:760
>  nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:593
>  nfsd_umount+0x48/0xe0 fs/nfsd/nfsctl.c:1347
>  deactivate_locked_super+0xc1/0x1a0 fs/super.c:473
>  deactivate_super fs/super.c:506 [inline]
>  deactivate_super+0xde/0x100 fs/super.c:502
>  cleanup_mnt+0x225/0x450 fs/namespace.c:1318
>  task_work_run+0x150/0x240 kernel/task_work.c:227
>  resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
>  exit_to_user_mode_loop+0xec/0x130 kernel/entry/common.c:43
>  exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
>  syscall_exit_to_user_mode_work include/linux/entry-common.h:175 
> [inline]
>  syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
>  do_syscall_64+0x426/0xfa0 arch/x86/entry/syscall_64.c:100
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f70f958f7c9
> RSP: 002b:00007f70fa3f9038 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
> RAX: fffffffffffffffe RBX: 00007f70f97e5fa0 RCX: 00007f70f958f7c9
> RDX: 0000200000000100 RSI: 00002000000000c0 RDI: 0000000000000000
> RBP: 00007f70f9613f91 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007f70f97e6038 R14: 00007f70f97e5fa0 R15: 00007ffd32d60018
>  </TASK>
>
> Showing all locks held in the system:
> 1 lock held by khungtaskd/31:
>  #0: ffffffff8e3c45e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire 
> include/linux/rcupdate.h:331 [inline]
>  #0: ffffffff8e3c45e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock 
> include/linux/rcupdate.h:867 [inline]
>  #0: ffffffff8e3c45e0 (rcu_read_lock){....}-{1:3}, at: 
> debug_show_all_locks+0x36/0x1c0 kernel/locking/lockdep.c:6775
> 2 locks held by kworker/1:4/5890:
>  #0: ffff88813ff15948 ((wq_completion)events){+.+.}-{0:0}, at: 
> process_one_work+0x12a2/0x1b70 kernel/workqueue.c:3238
>  #1: ffffc9000456fd00 (free_ipc_work){+.+.}-{0:0}, at: 
> process_one_work+0x929/0x1b70 kernel/workqueue.c:3239
> 2 locks held by kworker/u10:4/13138:
>  #0: ffff88813ff29148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: 
> process_one_work+0x12a2/0x1b70 kernel/workqueue.c:3238
>  #1: ffff8880b8524088 (psi_seq){-.-.}-{0:0}, at: psi_sched_switch 
> kernel/sched/stats.h:220 [inline]
>  #1: ffff8880b8524088 (psi_seq){-.-.}-{0:0}, at: 
> __schedule+0x1861/0x5de0 kernel/sched/core.c:6923
> 2 locks held by syz.4.1989/15528:
>  #0: ffff88806018e0e0 (&type->s_umount_key#52){++++}-{4:4}, at: 
> __super_lock fs/super.c:57 [inline]
>  #0: ffff88806018e0e0 (&type->s_umount_key#52){++++}-{4:4}, at: 
> __super_lock_excl fs/super.c:72 [inline]
>  #0: ffff88806018e0e0 (&type->s_umount_key#52){++++}-{4:4}, at: 
> deactivate_super fs/super.c:505 [inline]
>  #0: ffff88806018e0e0 (&type->s_umount_key#52){++++}-{4:4}, at: 
> deactivate_super+0xd6/0x100 fs/super.c:502
>  #1: ffffffff8e7ed348 (nfsd_mutex){+.+.}-{4:4}, at: 
> nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:593
> 5 locks held by kworker/u10:10/18292:
>  #0: ffff88801ba9f148 ((wq_completion)netns){+.+.}-{0:0}, at: 
> process_one_work+0x12a2/0x1b70 kernel/workqueue.c:3238
>  #1: ffffc90004a9fd00 (net_cleanup_work){+.+.}-{0:0}, at: 
> process_one_work+0x929/0x1b70 kernel/workqueue.c:3239
>  #2: ffffffff900d52b0 (pernet_ops_rwsem){++++}-{4:4}, at: 
> cleanup_net+0xad/0x8b0 net/core/net_namespace.c:669
>  #3: ffffffff900eb6c8 (rtnl_mutex){+.+.}-{4:4}, at: 
> wiphy_unregister+0x13d/0xc50 net/wireless/core.c:1165
>  #4: ffff88805dad0788 (&rdev->wiphy.mtx){+.+.}-{4:4}, at: wiphy_lock 
> include/net/cfg80211.h:6343 [inline]
>  #4: ffff88805dad0788 (&rdev->wiphy.mtx){+.+.}-{4:4}, at: 
> wiphy_unregister+0x147/0xc50 net/wireless/core.c:1166
> 3 locks held by kworker/u10:12/18294:
>  #0: ffff888030d69948 ((wq_completion)ipv6_addrconf){+.+.}-{0:0}, at: 
> process_one_work+0x12a2/0x1b70 kernel/workqueue.c:3238
>  #1: ffffc90003eefd00 
> ((work_completion)(&(&net->ipv6.addr_chk_work)->work)){+.+.}-{0:0}, at: 
> process_one_work+0x929/0x1b70 kernel/workqueue.c:3239
>  #2: ffffffff900eb6c8 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_net_lock 
> include/linux/rtnetlink.h:130 [inline]
>  #2: ffffffff900eb6c8 (rtnl_mutex){+.+.}-{4:4}, at: 
> addrconf_verify_work+0x12/0x30 net/ipv6/addrconf.c:4734
> 1 lock held by syz.1.2823/19276:
> 2 locks held by syz.5.2942/19853:
>  #0: ffffffff9018f490 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 
> net/netlink/genetlink.c:1218
>  #1: ffffffff8e7ed348 (nfsd_mutex){+.+.}-{4:4}, at: 
> nfsd_nl_threads_set_doit+0x687/0xbc0 fs/nfsd/nfsctl.c:1590
> 2 locks held by getty/20629:
>  #0: ffff88803528d0a0 (&tty->ldisc_sem){++++}-{0:0}, at: 
> tty_ldisc_ref_wait+0x24/0x80 drivers/tty/tty_ldisc.c:243
>  #1: ffffc90002fd22f0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: 
> n_tty_read+0x41b/0x14f0 drivers/tty/n_tty.c:2222
> 2 locks held by syz.7.3138/20679:
>  #0: ffffffff9018f490 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 
> net/netlink/genetlink.c:1218
>  #1: ffffffff8e7ed348 (nfsd_mutex){+.+.}-{4:4}, at: 
> nfsd_nl_version_set_doit+0xc4/0x7a0 fs/nfsd/nfsctl.c:1730
> 2 locks held by syz.6.3144/20706:
>  #0: ffff88805a2600e0 (&type->s_umount_key#52){++++}-{4:4}, at: 
> __super_lock fs/super.c:57 [inline]
>  #0: ffff88805a2600e0 (&type->s_umount_key#52){++++}-{4:4}, at: 
> __super_lock_excl fs/super.c:72 [inline]
>  #0: ffff88805a2600e0 (&type->s_umount_key#52){++++}-{4:4}, at: 
> deactivate_super fs/super.c:505 [inline]
>  #0: ffff88805a2600e0 (&type->s_umount_key#52){++++}-{4:4}, at: 
> deactivate_super+0xd6/0x100 fs/super.c:502
>  #1: ffffffff8e7ed348 (nfsd_mutex){+.+.}-{4:4}, at: 
> nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:593
> 2 locks held by syz-executor/20776:
>  #0: ffff88805b41e0e0 (&type->s_umount_key#52){++++}-{4:4}, at: 
> __super_lock fs/super.c:57 [inline]
>  #0: ffff88805b41e0e0 (&type->s_umount_key#52){++++}-{4:4}, at: 
> __super_lock_excl fs/super.c:72 [inline]
>  #0: ffff88805b41e0e0 (&type->s_umount_key#52){++++}-{4:4}, at: 
> deactivate_super fs/super.c:505 [inline]
>  #0: ffff88805b41e0e0 (&type->s_umount_key#52){++++}-{4:4}, at: 
> deactivate_super+0xd6/0x100 fs/super.c:502
>  #1: ffffffff8e7ed348 (nfsd_mutex){+.+.}-{4:4}, at: 
> nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:593
> 2 locks held by syz.2.3203/21060:
>  #0: ffff88801c3480e0 (&type->s_umount_key#52){++++}-{4:4}, at: 
> __super_lock fs/super.c:57 [inline]
>  #0: ffff88801c3480e0 (&type->s_umount_key#52){++++}-{4:4}, at: 
> __super_lock_excl fs/super.c:72 [inline]
>  #0: ffff88801c3480e0 (&type->s_umount_key#52){++++}-{4:4}, at: 
> deactivate_super fs/super.c:505 [inline]
>  #0: ffff88801c3480e0 (&type->s_umount_key#52){++++}-{4:4}, at: 
> deactivate_super+0xd6/0x100 fs/super.c:502
>  #1: ffffffff8e7ed348 (nfsd_mutex){+.+.}-{4:4}, at: 
> nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:593
> 2 locks held by syz.3.3291/21497:
>  #0: ffff8880753ce0e0 (&type->s_umount_key#52){++++}-{4:4}, at: 
> __super_lock fs/super.c:57 [inline]
>  #0: ffff8880753ce0e0 (&type->s_umount_key#52){++++}-{4:4}, at: 
> __super_lock_excl fs/super.c:72 [inline]
>  #0: ffff8880753ce0e0 (&type->s_umount_key#52){++++}-{4:4}, at: 
> deactivate_super fs/super.c:505 [inline]
>  #0: ffff8880753ce0e0 (&type->s_umount_key#52){++++}-{4:4}, at: 
> deactivate_super+0xd6/0x100 fs/super.c:502
>  #1: ffffffff8e7ed348 (nfsd_mutex){+.+.}-{4:4}, at: 
> nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:593
> 2 locks held by syz-executor/21510:
>  #0: ffffffff8f492c00 (&ops->srcu#2){.+.+}-{0:0}, at: srcu_lock_acquire 
> include/linux/srcu.h:161 [inline]
>  #0: ffffffff8f492c00 (&ops->srcu#2){.+.+}-{0:0}, at: srcu_read_lock 
> include/linux/srcu.h:253 [inline]
>  #0: ffffffff8f492c00 (&ops->srcu#2){.+.+}-{0:0}, at: 
> rtnl_link_ops_get+0x113/0x2c0 net/core/rtnetlink.c:574
>  #1: ffffffff900eb6c8 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock 
> net/core/rtnetlink.c:80 [inline]
>  #1: ffffffff900eb6c8 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_nets_lock 
> net/core/rtnetlink.c:341 [inline]
>  #1: ffffffff900eb6c8 (rtnl_mutex){+.+.}-{4:4}, at: 
> rtnl_newlink+0x600/0x2000 net/core/rtnetlink.c:4064
> 1 lock held by syz.9.3298/21533:
>  #0: ffffffff8e3cfb78 (rcu_state.exp_mutex){+.+.}-{4:4}, at: 
> exp_funnel_lock+0x1a3/0x3c0 kernel/rcu/tree_exp.h:343
> 5 locks held by syz.8.3302/21552:
>  #0: ffff8880334d0dc8 (&hdev->req_lock){+.+.}-{4:4}, at: 
> hci_dev_do_close+0x26/0x90 net/bluetooth/hci_core.c:499
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
>
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
>
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
>
> If you want to undo deduplication, reply with:
> #syz undup

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git nfsd-testing

-- 
Chuck Lever

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