[v6.1] INFO: task hung in nfsd_nrthreads

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: dc5c83b7f5f8 Linux 6.1.178
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=13521499580000
kernel config: https://syzkaller.appspot.com/x/.config?x=872c04466179833f
dashboard link: https://syzkaller.appspot.com/bug?extid=3fdbad09fc1abd5f7da5
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
userspace arch: arm64

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/96393e4697a3/disk-dc5c83b7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0d4afce44fab/vmlinux-dc5c83b7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4787e310d875/Image-dc5c83b7.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3fdbad...@syzkaller.appspotmail.com

INFO: task syz.1.142:4791 blocked for more than 143 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.1.142 state:D stack:0 pid:4791 ppid:4330 flags:0x00000001
Call trace:
__switch_to+0x2f4/0x550 arch/arm64/kernel/process.c:555
context_switch kernel/sched/core.c:5246 [inline]
__schedule+0xdb4/0x1a6c kernel/sched/core.c:6563
schedule+0xc4/0x170 kernel/sched/core.c:6639
schedule_preempt_disabled+0x18/0x2c kernel/sched/core.c:6698
__mutex_lock_common+0xb20/0x1f3c kernel/locking/mutex.c:679
__mutex_lock kernel/locking/mutex.c:747 [inline]
mutex_lock_nested+0x38/0x44 kernel/locking/mutex.c:799
nfsd_nrthreads+0x58/0xfc fs/nfsd/nfssvc.c:280
write_threads+0x1c0/0x310 fs/nfsd/nfsctl.c:428
nfsctl_transaction_write+0x114/0x164 fs/nfsd/nfsctl.c:114
vfs_write+0x2a8/0x7c8 fs/read_write.c:582
ksys_write+0x12c/0x228 fs/read_write.c:637
__do_sys_write fs/read_write.c:649 [inline]
__se_sys_write fs/read_write.c:646 [inline]
__arm64_sys_write+0x7c/0x90 fs/read_write.c:646
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140
do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204
el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585
INFO: task syz.4.243:5033 blocked for more than 144 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.4.243 state:D stack:0 pid:5033 ppid:4341 flags:0x00000001
Call trace:
__switch_to+0x2f4/0x550 arch/arm64/kernel/process.c:555
context_switch kernel/sched/core.c:5246 [inline]
__schedule+0xdb4/0x1a6c kernel/sched/core.c:6563
schedule+0xc4/0x170 kernel/sched/core.c:6639
schedule_preempt_disabled+0x18/0x2c kernel/sched/core.c:6698
__mutex_lock_common+0xb20/0x1f3c kernel/locking/mutex.c:679
__mutex_lock kernel/locking/mutex.c:747 [inline]
mutex_lock_nested+0x38/0x44 kernel/locking/mutex.c:799
write_versions+0xa4/0xa34 fs/nfsd/nfsctl.c:681
nfsctl_transaction_write+0x114/0x164 fs/nfsd/nfsctl.c:114
vfs_write+0x2a8/0x7c8 fs/read_write.c:582
ksys_write+0x12c/0x228 fs/read_write.c:637
__do_sys_write fs/read_write.c:649 [inline]
__se_sys_write fs/read_write.c:646 [inline]
__arm64_sys_write+0x7c/0x90 fs/read_write.c:646
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140
do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204
el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

Showing all locks held in the system:
1 lock held by rcu_tasks_kthre/12:
#0: ffff800015557db0 (rcu_tasks.tasks_gp_mutex){+.+.}-{3:3}, at: rcu_tasks_one_gp+0x40/0xc48 kernel/rcu/tasks.h:517
1 lock held by rcu_tasks_trace/13:
#0: ffff8000155585d0 (rcu_tasks_trace.tasks_gp_mutex){+.+.}-{3:3}, at: rcu_tasks_one_gp+0x40/0xc48 kernel/rcu/tasks.h:517
1 lock held by khungtaskd/28:
#0: ffff800015557440 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0xc/0x44 include/linux/rcupdate.h:349
1 lock held by syslogd/3926:
#0: ffff00019f3c8398 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested kernel/sched/core.c:538 [inline]
#0: ffff00019f3c8398 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock kernel/sched/sched.h:1362 [inline]
#0: ffff00019f3c8398 (&rq->__lock){-.-.}-{2:2}, at: rq_lock kernel/sched/sched.h:1652 [inline]
#0: ffff00019f3c8398 (&rq->__lock){-.-.}-{2:2}, at: __schedule+0x2bc/0x1a6c kernel/sched/core.c:6479
2 locks held by getty/4084:
#0: ffff0000d674d098 (&tty->ldisc_sem){++++}-{0:0}, at: ldsem_down_read+0x3c/0x4c drivers/tty/tty_ldsem.c:340
#1: ffff80002093e2f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x2e8/0xfa8 drivers/tty/n_tty.c:2198
3 locks held by syz.1.142/4790:
#0: ffff0000d0b6dc68 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x118/0x17c fs/file.c:1038
#1: ffff0000d293a460 (sb_writers#13){.+.+}-{0:0}, at: vfs_write+0x254/0x7c8 fs/read_write.c:580
#2: ffff8000157e3f68 (nfsd_mutex){+.+.}-{3:3}, at: write_ports+0xbc/0x9f0 fs/nfsd/nfsctl.c:846
3 locks held by syz.1.142/4791:
#0: ffff0000d1cdcae8 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x118/0x17c fs/file.c:1038
#1: ffff0000d293a460 (sb_writers#13){.+.+}-{0:0}, at: vfs_write+0x254/0x7c8 fs/read_write.c:580
#2: ffff8000157e3f68 (nfsd_mutex){+.+.}-{3:3}, at: nfsd_nrthreads+0x58/0xfc fs/nfsd/nfssvc.c:280
3 locks held by kworker/u4:8/4842:
3 locks held by syz.4.243/5033:
#0: ffff0000d9d50d68 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x118/0x17c fs/file.c:1038
#1: ffff0000d9dca460 (sb_writers#13){.+.+}-{0:0}, at: vfs_write+0x254/0x7c8 fs/read_write.c:580
#2: ffff8000157e3f68 (nfsd_mutex){+.+.}-{3:3}, at: write_versions+0xa4/0xa34 fs/nfsd/nfsctl.c:681
2 locks held by kworker/u4:14/5271:
2 locks held by syz.3.349/5369:
#0: ffff0000d2e3c0e0 (&type->s_umount_key#50){+.+.}-{3:3}, at: deactivate_super+0xdc/0x104 fs/super.c:362
#1: ffff8000157e3f68 (nfsd_mutex){+.+.}-{3:3}, at: nfsd_shutdown_threads+0x60/0x204 fs/nfsd/nfssvc.c:633
1 lock held by syz.0.1104/8404:
#0: ffff00010629dc10 (&sb->s_type->i_mutex_key#12){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:758 [inline]
#0: ffff00010629dc10 (&sb->s_type->i_mutex_key#12){+.+.}-{3:3}, at: __sock_release net/socket.c:653 [inline]
#0: ffff00010629dc10 (&sb->s_type->i_mutex_key#12){+.+.}-{3:3}, at: sock_close+0x74/0x1ec net/socket.c:1400
1 lock held by rm/8422:

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