[syzbot] [nfs?] INFO: task hung in nfsd_umount

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 1dd28064d416 Merge tag 'integrity-v6.10-fix' of ssh://ra.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16814d76980000
kernel config: https://syzkaller.appspot.com/x/.config?x=1ace69f521989b1f
dashboard link: https://syzkaller.appspot.com/bug?extid=b568ba42c85a332a88ee
compiler: Debian clang version 15.0.6, 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/20c723869b92/disk-1dd28064.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c2a9a7382516/vmlinux-1dd28064.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9872fe6f2853/bzImage-1dd28064.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b568ba...@syzkaller.appspotmail.com

INFO: task syz.0.2871:13167 blocked for more than 143 seconds.
Not tainted 6.10.0-rc6-syzkaller-00212-g1dd28064d416 #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.2871 state:D stack:26704 pid:13167 tgid:13165 ppid:10304 flags:0x00000004
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5408 [inline]
__schedule+0x1796/0x49d0 kernel/sched/core.c:6745
__schedule_loop kernel/sched/core.c:6822 [inline]
schedule+0x14b/0x320 kernel/sched/core.c:6837
schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6894
__mutex_lock_common kernel/locking/mutex.c:684 [inline]
__mutex_lock+0x6a4/0xd70 kernel/locking/mutex.c:752
nfsd_shutdown_threads+0x4e/0xd0 fs/nfsd/nfssvc.c:632
nfsd_umount+0x43/0xd0 fs/nfsd/nfsctl.c:1412
deactivate_locked_super+0xc4/0x130 fs/super.c:473
put_fs_context+0x94/0x780 fs/fs_context.c:516
fscontext_release+0x65/0x80 fs/fsopen.c:73
__fput+0x24a/0x8a0 fs/file_table.c:422
task_work_run+0x24f/0x310 kernel/task_work.c:180
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
syscall_exit_to_user_mode+0x168/0x360 kernel/entry/common.c:218
do_syscall_64+0x100/0x230 arch/x86/entry/common.c:89
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f11fe775bd9
RSP: 002b:00007f11ff494048 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007f11fe903f60 RCX: 00007f11fe775bd9
RDX: 0000000000000000 RSI: ffffffffffffffff RDI: 0000000000000003
RBP: 00007f11fe7e4aa1 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007f11fe903f60 R15: 00007ffc04bba328
</TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/30:
#0: ffffffff8e333f20 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:329 [inline]
#0: ffffffff8e333f20 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:781 [inline]
#0: ffffffff8e333f20 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x55/0x2a0 kernel/locking/lockdep.c:6614
3 locks held by kworker/u8:4/66:
#0: ffff888015089148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3223 [inline]
#0: ffff888015089148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_scheduled_works+0x90a/0x1830 kernel/workqueue.c:3329
#1: ffffc900020afd00 ((work_completion)(&map->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3224 [inline]
#1: ffffc900020afd00 ((work_completion)(&map->work)){+.+.}-{0:0}, at: process_scheduled_works+0x945/0x1830 kernel/workqueue.c:3329
#2: ffffffff8e3391c0 (rcu_state.barrier_mutex){+.+.}-{3:3}, at: rcu_barrier+0x4c/0x530 kernel/rcu/tree.c:4448
4 locks held by udevd/4534:
#0: ffff88805a0fdd58 (&p->lock){+.+.}-{3:3}, at: seq_read_iter+0xb7/0xd60 fs/seq_file.c:182
#1: ffff88806542ec88 (&of->mutex#2){+.+.}-{3:3}, at: kernfs_seq_start+0x53/0x3b0 fs/kernfs/file.c:154
#2: ffff88805af532d8 (kn->active#5){++++}-{0:0}, at: kernfs_seq_start+0x72/0x3b0 fs/kernfs/file.c:155
#3: ffff8880686c90e8 (&dev->mutex){....}-{3:3}, at: device_lock include/linux/device.h:1009 [inline]
#3: ffff8880686c90e8 (&dev->mutex){....}-{3:3}, at: uevent_show+0x17d/0x340 drivers/base/core.c:2743
2 locks held by getty/4842:
#0: ffff88802f9d10a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
#1: ffffc9000312b2f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x6b5/0x1e10 drivers/tty/n_tty.c:2211
3 locks held by kworker/u9:10/5101:
#0: ffff88802e1fa148 ((wq_completion)hci2){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3223 [inline]
#0: ffff88802e1fa148 ((wq_completion)hci2){+.+.}-{0:0}, at: process_scheduled_works+0x90a/0x1830 kernel/workqueue.c:3329
#1: ffffc90003827d00 ((work_completion)(&hdev->cmd_sync_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3224 [inline]
#1: ffffc90003827d00 ((work_completion)(&hdev->cmd_sync_work)){+.+.}-{0:0}, at: process_scheduled_works+0x945/0x1830 kernel/workqueue.c:3329
#2: ffff888020eb4d88 (&hdev->req_lock){+.+.}-{3:3}, at: hci_cmd_sync_work+0x1ec/0x400 net/bluetooth/hci_sync.c:322
2 locks held by syz.4.2691/12623:
#0: ffffffff8f63ad70 (cb_lock){++++}-{3:3}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1218
#1: ffffffff8e5fff48 (nfsd_mutex){+.+.}-{3:3}, at: nfsd_nl_listener_set_doit+0x12d/0x1a90 fs/nfsd/nfsctl.c:1940
2 locks held by syz.0.2871/13167:
#0: ffff88804e1920e0 (&type->s_umount_key#77){++++}-{3:3}, at: __super_lock fs/super.c:56 [inline]
#0: ffff88804e1920e0 (&type->s_umount_key#77){++++}-{3:3}, at: __super_lock_excl fs/super.c:71 [inline]
#0: ffff88804e1920e0 (&type->s_umount_key#77){++++}-{3:3}, at: deactivate_super+0xb5/0xf0 fs/super.c:505
#1: ffffffff8e5fff48 (nfsd_mutex){+.+.}-{3:3}, at: nfsd_shutdown_threads+0x4e/0xd0 fs/nfsd/nfssvc.c:632
1 lock held by udevd/14823:
2 locks held by syz-executor/15993:
#0: ffffffff8f5d4908 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_lock net/core/rtnetlink.c:79 [inline]
#0: ffffffff8f5d4908 (rtnl_mutex){+.+.}-{3:3}, at: rtnetlink_rcv_msg+0x842/0x1180 net/core/rtnetlink.c:6632
#1: ffffffff8e3392f8 (rcu_state.exp_mutex){+.+.}-{3:3}, at: exp_funnel_lock kernel/rcu/tree_exp.h:323 [inline]
#1: ffffffff8e3392f8 (rcu_state.exp_mutex){+.+.}-{3:3}, at: synchronize_rcu_expedited+0x451/0x830 kernel/rcu/tree_exp.h:939
1 lock held by syz.4.3895/16063:
#0: ffff88804e1920e0 (&type->s_umount_key#77){++++}-{3:3}, at: __super_lock fs/super.c:58 [inline]
#0: ffff88804e1920e0 (&type->s_umount_key#77){++++}-{3:3}, at: super_lock+0x27c/0x400 fs/super.c:120
4 locks held by kvm-nx-lpage-re/16077:
#0: ffffffff8e361f28 (cgroup_mutex){+.+.}-{3:3}, at: cgroup_lock include/linux/cgroup.h:368 [inline]
#0: ffffffff8e361f28 (cgroup_mutex){+.+.}-{3:3}, at: cgroup_attach_task_all+0x27/0xe0 kernel/cgroup/cgroup-v1.c:61
#1: ffffffff8e1ce5b0 (cpu_hotplug_lock){++++}-{0:0}, at: cgroup_attach_lock+0x11/0x40 kernel/cgroup/cgroup.c:2413
#2: ffffffff8e362110 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: cgroup_attach_task_all+0x31/0xe0 kernel/cgroup/cgroup-v1.c:62
#3: ffffffff8e3392f8 (rcu_state.exp_mutex){+.+.}-{3:3}, at: exp_funnel_lock kernel/rcu/tree_exp.h:291 [inline]
#3: ffffffff8e3392f8 (rcu_state.exp_mutex){+.+.}-{3:3}, at: synchronize_rcu_expedited+0x381/0x830 kernel/rcu/tree_exp.h:939

=============================================

NMI backtrace for cpu 1
CPU: 1 PID: 30 Comm: khungtaskd Not tainted 6.10.0-rc6-syzkaller-00212-g1dd28064d416 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
nmi_cpu_backtrace+0x49c/0x4d0 lib/nmi_backtrace.c:113
nmi_trigger_cpumask_backtrace+0x198/0x320 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:162 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:223 [inline]
watchdog+0xfde/0x1020 kernel/hung_task.c:379
kthread+0x2f0/0x390 kernel/kthread.c:389
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
</TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 1109 Comm: kworker/u8:6 Not tainted 6.10.0-rc6-syzkaller-00212-g1dd28064d416 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
Workqueue: writeback wb_workfn (flush-8:0)
RIP: 0010:bio_add_page+0xb7/0x840 block/bio.c:1118
Code: 05 00 00 8b 5d 00 45 89 f4 41 f7 d4 89 df 44 89 e6 e8 dd 6f 11 fd 44 39 e3 76 0a e8 13 6e 11 fd e9 20 04 00 00 48 89 6c 24 28 <49> 8d 5f 70 48 89 d8 48 c1 e8 03 48 89 44 24 30 42 0f b6 04 28 84
RSP: 0018:ffffc900045ce610 EFLAGS: 00000213
RAX: 0000000000000000 RBX: 000000000000a000 RCX: ffff888022311e00
RDX: ffff888022311e00 RSI: 00000000ffffefff RDI: 000000000000a000
RBP: ffff88802eb37a28 R08: ffffffff8484b8a3 R09: 1ffffd4000090b30
R10: dffffc0000000000 R11: fffff94000090b31 R12: 00000000ffffefff
R13: dffffc0000000000 R14: 0000000000001000 R15: ffff88802eb37a00
FS: 0000000000000000(0000) GS:ffff8880b9400000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b30e11ff8 CR3: 000000000e132000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<NMI>
</NMI>
<TASK>
bio_add_folio+0x52/0x80 block/bio.c:1160
io_submit_add_bh fs/ext4/page-io.c:422 [inline]
ext4_bio_write_folio+0x1691/0x1da0 fs/ext4/page-io.c:560
mpage_submit_folio+0x1af/0x230 fs/ext4/inode.c:1869
mpage_process_page_bufs+0x6c9/0x8d0 fs/ext4/inode.c:1982
mpage_prepare_extent_to_map+0xec7/0x1c80 fs/ext4/inode.c:2490
ext4_do_writepages+0xc52/0x3d40 fs/ext4/inode.c:2632
ext4_writepages+0x213/0x3c0 fs/ext4/inode.c:2768
do_writepages+0x359/0x870 mm/page-writeback.c:2656
__writeback_single_inode+0x165/0x10b0 fs/fs-writeback.c:1651
writeback_sb_inodes+0x99c/0x1380 fs/fs-writeback.c:1947
__writeback_inodes_wb+0x11b/0x260 fs/fs-writeback.c:2018
wb_writeback+0x495/0xd40 fs/fs-writeback.c:2129
wb_check_old_data_flush fs/fs-writeback.c:2233 [inline]
wb_do_writeback fs/fs-writeback.c:2286 [inline]
wb_workfn+0xba1/0x1090 fs/fs-writeback.c:2314
process_one_work kernel/workqueue.c:3248 [inline]
process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3329
worker_thread+0x86d/0xd50 kernel/workqueue.c:3409
kthread+0x2f0/0x390 kernel/kthread.c:389
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
</TASK>


---
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 syzk...@googlegroups.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

[Jeff Layton]

Above there are two tasks that are holding/blocked on the nfsd_mutex.
The first is the stuck thread. The second is a task that took it in
nfsd_nl_listener_set_doit. I don't see a way to exit that function
without releasing that mutex, so it seems likely that thread is stuck
too for some reason. Unfortunately, we don't have a stack trace from
that task, so I can't tell what it's doing.

--
Jeff Layton <jla...@kernel.org>

[NeilBrown]

On Sun, 07 Jul 2024, Jeff Layton wrote:
> On Sat, 2024-07-06 at 21:37 -0700, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit: 1dd28064d416 Merge tag 'integrity-v6.10-fix' of ssh://ra.k..

...

> > 2 locks held by syz.4.2691/12623:
> > #0: ffffffff8f63ad70 (cb_lock){++++}-{3:3}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1218
> > #1: ffffffff8e5fff48 (nfsd_mutex){+.+.}-{3:3}, at: nfsd_nl_listener_set_doit+0x12d/0x1a90 fs/nfsd/nfsctl.c:1940
> > 2 locks held by syz.0.2871/13167:
> > #0: ffff88804e1920e0 (&type->s_umount_key#77){++++}-{3:3}, at: __super_lock fs/super.c:56 [inline]
> > #0: ffff88804e1920e0 (&type->s_umount_key#77){++++}-{3:3}, at: __super_lock_excl fs/super.c:71 [inline]
> > #0: ffff88804e1920e0 (&type->s_umount_key#77){++++}-{3:3}, at: deactivate_super+0xb5/0xf0 fs/super.c:505
> > #1: ffffffff8e5fff48 (nfsd_mutex){+.+.}-{3:3}, at: nfsd_shutdown_threads+0x4e/0xd0 fs/nfsd/nfssvc.c:632
>
> Above there are two tasks that are holding/blocked on the nfsd_mutex.
> The first is the stuck thread. The second is a task that took it in
> nfsd_nl_listener_set_doit. I don't see a way to exit that function
> without releasing that mutex, so it seems likely that thread is stuck
> too for some reason. Unfortunately, we don't have a stack trace from
> that task, so I can't tell what it's doing.
>

We can guess though. It isn't waiting for a lock - that would show in
the above list - so it might be waiting for a wakeup, or might be
spinning.
The only wake-up I can imagine is in one of the memory-allocation calls,
but if the system were running out of memory we would probably see
messages about that.

I wonder if it could be looping in svc_xprt_destroy_all(), and sitting
in the msleep() when the hang is detected so there are no locks to
report. I can't see while it would block there.

It would really help to get a full task list.
There is a sysctl for that: /proc/sys/kernel/hung_task_all_cpu_backtrace

Could that be enabled?

NeilBrown

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: 3eb40771c00a Merge tag 'soc-fixes-7.2-3' of git://git.kern..
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=1309ba79580000
kernel config: https://syzkaller.appspot.com/x/.config?x=1d67342c314f228d
dashboard link: https://syzkaller.appspot.com/bug?extid=b568ba42c85a332a88ee
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=156daa25580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13ad9a79580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/21569197c3cb/disk-3eb40771.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/09af5299a851/vmlinux-3eb40771.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c657b46695b7/bzImage-3eb40771.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b568ba...@syzkaller.appspotmail.com

INFO: task syz-executor347:5620 blocked for more than 143 seconds.
Not tainted syzkaller #0

"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

task:syz-executor347 state:D stack:22184 pid:5620 tgid:5620 ppid:5617 task_flags:0x400140 flags:0x00080001
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5510 [inline]
__schedule+0x125c/0x6730 kernel/sched/core.c:7234
__schedule_loop kernel/sched/core.c:7311 [inline]
schedule+0xdd/0x2c0 kernel/sched/core.c:7326
schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7383
__mutex_lock_common kernel/locking/mutex.c:726 [inline]
__mutex_lock+0xccc/0x1bd0 kernel/locking/mutex.c:821
nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
nfsd_umount+0x3b/0x60 fs/nfsd/nfsctl.c:1365
deactivate_locked_super+0xc1/0x1b0 fs/super.c:477
deactivate_super fs/super.c:510 [inline]
deactivate_super+0xe7/0x110 fs/super.c:506
cleanup_mnt+0x21f/0x450 fs/namespace.c:1317
task_work_run+0x150/0x240 kernel/task_work.c:233
ptrace_notify+0xf3/0x120 kernel/signal.c:2531
ptrace_report_syscall include/linux/ptrace.h:416 [inline]
ptrace_report_syscall_exit include/linux/ptrace.h:478 [inline]
arch_ptrace_report_syscall_exit include/linux/entry-common.h:213 [inline]
syscall_exit_work include/linux/entry-common.h:248 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:279 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:316 [inline]
do_syscall_64+0x6c0/0x870 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f056f6eec17
RSP: 002b:00007ffff209c618 EFLAGS: 00000206 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 000000000001399c RCX: 00007f056f6eec17
RDX: 0000000000000000 RSI: 0000000000000009 RDI: 00007ffff209c6d0
RBP: 00007ffff209c6d0 R08: 00007ffff209d6d0 R09: 00000000ffffffff
R10: 0000000000000000 R11: 0000000000000206 R12: 00007ffff209d740
R13: 0000555587301780 R14: 00007ffff209d740 R15: 0000000000000001
</TASK>
INFO: task syz-executor347:5775 blocked for more than 143 seconds.
Not tainted syzkaller #0

"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

task:syz-executor347 state:D stack:27448 pid:5775 tgid:5775 ppid:5618 task_flags:0x400140 flags:0x00080002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5510 [inline]
__schedule+0x125c/0x6730 kernel/sched/core.c:7234
__schedule_loop kernel/sched/core.c:7311 [inline]
schedule+0xdd/0x2c0 kernel/sched/core.c:7326
schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7383
__mutex_lock_common kernel/locking/mutex.c:726 [inline]
__mutex_lock+0xccc/0x1bd0 kernel/locking/mutex.c:821
write_ports+0xa5/0xcc0 fs/nfsd/nfsctl.c:860
nfsctl_transaction_write+0x106/0x1a0 fs/nfsd/nfsctl.c:112
vfs_write+0x2aa/0x1050 fs/read_write.c:685
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f056f6eea19
RSP: 002b:00007ffff209d708 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 645f6473666e2f2e RCX: 00007f056f6eea19
RDX: 0000000000000005 RSI: 0000200000000700 RDI: 0000000000000003
RBP: 0000000000000000 R08: 00007f056f75a222 R09: 00007f056f75a222
R10: 00007f056f75a222 R11: 0000000000000246 R12: 00007f056f75a47b
R13: 0000000000000001 R14: 00007ffff209d740 R15: 0000000000000000
</TASK>
INFO: task syz-executor347:5776 blocked for more than 143 seconds.
Not tainted syzkaller #0

"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

task:syz-executor347 state:D stack:27088 pid:5776 tgid:5776 ppid:5615 task_flags:0x400140 flags:0x00080002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5510 [inline]
__schedule+0x125c/0x6730 kernel/sched/core.c:7234
__schedule_loop kernel/sched/core.c:7311 [inline]
schedule+0xdd/0x2c0 kernel/sched/core.c:7326
schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7383
__mutex_lock_common kernel/locking/mutex.c:726 [inline]
__mutex_lock+0xccc/0x1bd0 kernel/locking/mutex.c:821
write_ports+0xa5/0xcc0 fs/nfsd/nfsctl.c:860
nfsctl_transaction_write+0x106/0x1a0 fs/nfsd/nfsctl.c:112
vfs_write+0x2aa/0x1050 fs/read_write.c:685
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f056f6eea19
RSP: 002b:00007ffff209d708 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 645f6473666e2f2e RCX: 00007f056f6eea19
RDX: 0000000000000005 RSI: 0000200000000700 RDI: 0000000000000003
RBP: 0000000000000000 R08: 00007f056f75a222 R09: 00007f056f75a222
R10: 00007f056f75a222 R11: 0000000000000246 R12: 00007f056f75a47b
R13: 0000000000000001 R14: 00007ffff209d740 R15: 0000000000000000
</TASK>
INFO: task syz-executor347:5777 blocked for more than 144 seconds.
Not tainted syzkaller #0

"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

task:syz-executor347 state:D stack:27848 pid:5777 tgid:5777 ppid:5614 task_flags:0x400140 flags:0x00080002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5510 [inline]
__schedule+0x125c/0x6730 kernel/sched/core.c:7234
__schedule_loop kernel/sched/core.c:7311 [inline]
schedule+0xdd/0x2c0 kernel/sched/core.c:7326
schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7383
__mutex_lock_common kernel/locking/mutex.c:726 [inline]
__mutex_lock+0xccc/0x1bd0 kernel/locking/mutex.c:821
write_ports+0xa5/0xcc0 fs/nfsd/nfsctl.c:860
nfsctl_transaction_write+0x106/0x1a0 fs/nfsd/nfsctl.c:112
vfs_write+0x2aa/0x1050 fs/read_write.c:685
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f056f6eea19
RSP: 002b:00007ffff209d708 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 645f6473666e2f2e RCX: 00007f056f6eea19
RDX: 0000000000000005 RSI: 0000200000000700 RDI: 0000000000000003
RBP: 0000000000000000 R08: 00007f056f75a222 R09: 00007f056f75a222
R10: 00007f056f75a222 R11: 0000000000000246 R12: 00007f056f75a47b
R13: 0000000000000001 R14: 00007ffff209d740 R15: 0000000000000000

</TASK>

Showing all locks held in the system:

1 lock held by khungtaskd/31:
#0: ffffffff8ede8200 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
#0: ffffffff8ede8200 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
#0: ffffffff8ede8200 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x3d/0x184 kernel/locking/lockdep.c:6775
5 locks held by kworker/u8:6/152:
2 locks held by getty/5348:
#0: ffff888037c7d0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x24/0x80 drivers/tty/tty_ldisc.c:243
#1: ffffc900032332e8 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x419/0x14e0 drivers/tty/n_tty.c:2211
2 locks held by syz-executor347/5619:
#0: ffff88806d1b80d8 (&type->s_umount_key#67){+.+.}-{4:4}, at: __super_lock fs/super.c:58 [inline]
#0: ffff88806d1b80d8 (&type->s_umount_key#67){+.+.}-{4:4}, at: __super_lock_excl fs/super.c:73 [inline]
#0: ffff88806d1b80d8 (&type->s_umount_key#67){+.+.}-{4:4}, at: deactivate_super fs/super.c:509 [inline]
#0: ffff88806d1b80d8 (&type->s_umount_key#67){+.+.}-{4:4}, at: deactivate_super+0xdf/0x110 fs/super.c:506
#1: ffffffff8f272480 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
2 locks held by syz-executor347/5620:
#0: ffff88806d2220d8 (&type->s_umount_key#67){+.+.}-{4:4}, at: __super_lock fs/super.c:58 [inline]
#0: ffff88806d2220d8 (&type->s_umount_key#67){+.+.}-{4:4}, at: __super_lock_excl fs/super.c:73 [inline]
#0: ffff88806d2220d8 (&type->s_umount_key#67){+.+.}-{4:4}, at: deactivate_super fs/super.c:509 [inline]
#0: ffff88806d2220d8 (&type->s_umount_key#67){+.+.}-{4:4}, at: deactivate_super+0xdf/0x110 fs/super.c:506
#1: ffffffff8f272480 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
2 locks held by syz-executor347/5775:
#0: ffff888079e4c450 (sb_writers#9){.+.+}-{0:0}, at: ksys_write+0x12a/0x250 fs/read_write.c:739
#1: ffffffff8f272480 (nfsd_mutex){+.+.}-{4:4}, at: write_ports+0xa5/0xcc0 fs/nfsd/nfsctl.c:860
2 locks held by syz-executor347/5776:
#0: ffff88807af5e450 (sb_writers#9){.+.+}-{0:0}, at: ksys_write+0x12a/0x250 fs/read_write.c:739
#1: ffffffff8f272480 (nfsd_mutex){+.+.}-{4:4}, at: write_ports+0xa5/0xcc0 fs/nfsd/nfsctl.c:860
2 locks held by syz-executor347/5777:
#0: ffff8880246f6450 (sb_writers#9){.+.+}-{0:0}, at: ksys_write+0x12a/0x250 fs/read_write.c:739
#1: ffffffff8f272480 (nfsd_mutex){+.+.}-{4:4}, at: write_ports+0xa5/0xcc0 fs/nfsd/nfsctl.c:860

=============================================

NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 31 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT(full)
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:122
nmi_trigger_cpumask_backtrace+0x21c/0x2a0 lib/nmi_backtrace.c:65
trigger_all_cpu_backtrace include/linux/nmi.h:162 [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+0x370/0x450 kernel/kthread.c:436
ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
Sending NMI from CPU 0 to CPUs 1:

NMI backtrace for cpu 1

CPU: 1 UID: 0 PID: 13 Comm: kworker/u8:1 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Workqueue: bat_events batadv_mcast_mla_update
RIP: 0010:_static_cpu_has arch/x86/include/asm/cpufeature.h:101 [inline]
RIP: 0010:addr_has_metadata mm/kasan/kasan.h:334 [inline]
RIP: 0010:check_region_inline mm/kasan/generic.c:188 [inline]
RIP: 0010:kasan_check_range+0x31/0x1e0 mm/kasan/generic.c:200
Code: 0f 84 7a 01 00 00 48 89 f8 41 54 41 89 d0 48 01 f0 55 53 0f 82 e6 00 00 00 eb 0f cc cc cc 48 b8 00 00 00 00 00 00 00 ff eb 0a <48> b8 00 00 00 00 00 80 ff ff 48 39 c7 0f 82 c2 00 00 00 4c 8d 54
RSP: 0018:ffffc90000127a60 EFLAGS: 00000282
RAX: ffffc90000127b34 RBX: ffffc90000127b30 RCX: ffffffff8b8815dd
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffc90000127b30
RBP: 0000000000000004 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: ffff88807832d8a8 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff888123cde000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00005620a0b86660 CR3: 000000000eb94000 CR4: 00000000003526f0
Call Trace:
<TASK>
__asan_memset+0x23/0x50 mm/kasan/shadow.c:84
batadv_mcast_mla_flags_get net/batman-adv/multicast.c:283 [inline]
__batadv_mcast_mla_update net/batman-adv/multicast.c:907 [inline]
batadv_mcast_mla_update+0x10d/0x3200 net/batman-adv/multicast.c:946
process_one_work+0xa23/0x1940 kernel/workqueue.c:3322
process_scheduled_works kernel/workqueue.c:3405 [inline]
worker_thread+0x5ef/0xe50 kernel/workqueue.c:3486
kthread+0x370/0x450 kernel/kthread.c:436
ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.