syzbot
INFO: task hung in nfsd_svc
Status:
upstream: reported on 2026/07/27 20:24
Reported-by: syzbot+3af7fc658946546571d0@syzkaller.appspotmail.com
First crash: 34d, last: 9d03h
Sample crash report:
INFO: task syz.3.559:8094 blocked for more than 143 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.3.559 state:D stack:26832 pid:8094 ppid:5772 flags:0x00004004
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5382 [inline]
__schedule+0x15ae/0x4660 kernel/sched/core.c:6701
schedule+0xbd/0x170 kernel/sched/core.c:6775
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:6834
__mutex_lock_common kernel/locking/mutex.c:679 [inline]
__mutex_lock+0x673/0xc80 kernel/locking/mutex.c:747
nfsd_svc+0x65/0xab0 fs/nfsd/nfssvc.c:788
write_threads+0x393/0x510 fs/nfsd/nfsctl.c:417
nfsctl_transaction_write+0x10c/0x150 fs/nfsd/nfsctl.c:113
vfs_write+0x299/0x9a0 fs/read_write.c:582
ksys_write+0x151/0x260 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f722ef9e0d9
RSP: 002b:00007f722fe5f028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f722f226090 RCX: 00007f722ef9e0d9
RDX: 0000000000000002 RSI: 0000200000000900 RDI: 0000000000000003
RBP: 00007f722f035024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f722f226128 R14: 00007f722f226090 R15: 00007ffdd5f8f348
</TASK>
Showing all locks held in the system:
2 locks held by ksoftirqd/0/16:
4 locks held by kworker/1:0/23:
#0: ffff888147251538 ((wq_completion)md_misc){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2632 [inline]
#0: ffff888147251538 ((wq_completion)md_misc){+.+.}-{0:0}, at: process_scheduled_works+0x975/0x1600 kernel/workqueue.c:2734
#1: ffffc900001d7d00 ((work_completion)(&mddev->del_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2632 [inline]
#1: ffffc900001d7d00 ((work_completion)(&mddev->del_work)){+.+.}-{0:0}, at: process_scheduled_works+0x975/0x1600 kernel/workqueue.c:2734
#2: ffff8880b8e3c298 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x9c/0x130 kernel/sched/core.c:567
#3: ffffffff8d131da0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
#3: ffffffff8d131da0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:786 [inline]
#3: ffffffff8d131da0 (rcu_read_lock){....}-{1:2}, at: xa_load+0x64/0x2e0 lib/xarray.c:1459
1 lock held by khungtaskd/29:
#0: ffffffff8d131da0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
#0: ffffffff8d131da0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:786 [inline]
#0: ffffffff8d131da0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x55/0x290 kernel/locking/lockdep.c:6633
2 locks held by getty/5529:
#0: ffff88814ccd10a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
#1: ffffc9000327b2f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x428/0x1370 drivers/tty/n_tty.c:2217
2 locks held by kworker/0:3/5780:
#0: ffff888017c72d38 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2632 [inline]
#0: ffff888017c72d38 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: process_scheduled_works+0x975/0x1600 kernel/workqueue.c:2734
#1: ffffc900047afd00 ((work_completion)(&rew->rew_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2632 [inline]
#1: ffffc900047afd00 ((work_completion)(&rew->rew_work)){+.+.}-{0:0}, at: process_scheduled_works+0x975/0x1600 kernel/workqueue.c:2734
1 lock held by syz-executor/7971:
3 locks held by kworker/u4:29/8042:
#0: ffff8880b8e3c298 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x9c/0x130 kernel/sched/core.c:567
#1: ffff8880b8e28a00 (psi_seq){-.-.}-{0:0}, at: psi_sched_switch kernel/sched/stats.h:189 [inline]
#1: ffff8880b8e28a00 (psi_seq){-.-.}-{0:0}, at: __schedule+0x21d3/0x4660 kernel/sched/core.c:6696
#2: ffff8880b8e295d8 (&base->lock){-.-.}-{2:2}, at: __mod_timer+0x6cf/0xd60 kernel/time/timer.c:1112
3 locks held by syz.3.559/8093:
#0: ffff888024ac20c8 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2a3/0x330 fs/file.c:1040
#1: ffff888050d28418 (sb_writers#28){.+.+}-{0:0}, at: vfs_write+0x21e/0x9a0 fs/read_write.c:580
#2: ffffffff8d3e1688 (nfsd_mutex){+.+.}-{3:3}, at: write_ports+0xb7/0xfa0 fs/nfsd/nfsctl.c:843
3 locks held by syz.3.559/8094:
#0: ffff888024ac2848 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x2a3/0x330 fs/file.c:1040
#1: ffff888050d28418 (sb_writers#28){.+.+}-{0:0}, at: vfs_write+0x21e/0x9a0 fs/read_write.c:580
#2: ffffffff8d3e1688 (nfsd_mutex){+.+.}-{3:3}, at: nfsd_svc+0x65/0xab0 fs/nfsd/nfssvc.c:788
1 lock held by syz.4.798/9278:
1 lock held by syz.2.807/9314:
2 locks held by dhcpcd/9336:
#0: ffff888076b63820 (&sb->s_type->i_mutex_key#11){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:804 [inline]
#0: ffff888076b63820 (&sb->s_type->i_mutex_key#11){+.+.}-{3:3}, at: __sock_release net/socket.c:658 [inline]
#0: ffff888076b63820 (&sb->s_type->i_mutex_key#11){+.+.}-{3:3}, at: sock_close+0x82/0x210 net/socket.c:1421
#1: ffffffff8d137778 (rcu_state.exp_mutex){+.+.}-{3:3}, at: exp_funnel_lock kernel/rcu/tree_exp.h:324 [inline]
#1: ffffffff8d137778 (rcu_state.exp_mutex){+.+.}-{3:3}, at: synchronize_rcu_expedited+0x3da/0x880 kernel/rcu/tree_exp.h:1004
2 locks held by dhcpcd/9339:
#0: ffff888076b64420 (&sb->s_type->i_mutex_key#11){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:804 [inline]
#0: ffff888076b64420 (&sb->s_type->i_mutex_key#11){+.+.}-{3:3}, at: __sock_release net/socket.c:658 [inline]
#0: ffff888076b64420 (&sb->s_type->i_mutex_key#11){+.+.}-{3:3}, at: sock_close+0x82/0x210 net/socket.c:1421
#1: ffffffff8d137778 (rcu_state.exp_mutex){+.+.}-{3:3}, at: exp_funnel_lock kernel/rcu/tree_exp.h:324 [inline]
#1: ffffffff8d137778 (rcu_state.exp_mutex){+.+.}-{3:3}, at: synchronize_rcu_expedited+0x3da/0x880 kernel/rcu/tree_exp.h:1004
=============================================
NMI backtrace for cpu 1
CPU: 1 PID: 29 Comm: khungtaskd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
<TASK>
dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
nmi_cpu_backtrace+0x3a6/0x3e0 lib/nmi_backtrace.c:113
nmi_trigger_cpumask_backtrace+0x17a/0x2f0 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:160 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:222 [inline]
watchdog+0xf59/0xfa0 kernel/hung_task.c:379
kthread+0x2fa/0x390 kernel/kthread.c:388
ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
</TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 9314 Comm: syz.2.807 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:kasan_mem_to_shadow include/linux/kasan.h:60 [inline]
RIP: 0010:memory_is_poisoned_n mm/kasan/generic.c:128 [inline]
RIP: 0010:memory_is_poisoned mm/kasan/generic.c:159 [inline]
RIP: 0010:check_region_inline mm/kasan/generic.c:178 [inline]
RIP: 0010:kasan_check_range+0x59/0x290 mm/kasan/generic.c:187
Code: f9 ff ff 01 00 0f 82 ff 01 00 00 49 89 ff 49 c1 ef 03 49 ba 00 00 00 00 00 fc ff df 4f 8d 1c 17 49 ff c8 4d 89 c1 49 c1 e9 03 <48> bb 01 00 00 00 00 fc ff df 4d 8d 34 19 4d 89 f4 4d 29 dc 49 83
RSP: 0018:ffffc900050766c8 EFLAGS: 00000803
RAX: 0000000000000001 RBX: 00000000000000b2 RCX: ffffffff816890ab
RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffffffff911ee510
RBP: ffffc90005076948 R08: ffffffff911ee517 R09: 1ffffffff223dca2
R10: dffffc0000000000 R11: fffffbfff223dca2 R12: 0000000000040000
R13: ffff888050425a00 R14: 0000000000000000 R15: 1ffffffff223dca2
FS: 00007f25d309a6c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055e9e6b78660 CR3: 0000000045cea000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 000000000000000e DR6: 00000000ffff0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
instrument_atomic_read include/linux/instrumented.h:68 [inline]
_test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
hlock_class kernel/locking/lockdep.c:228 [inline]
check_wait_context kernel/locking/lockdep.c:4774 [inline]
__lock_acquire+0x61b/0x7d80 kernel/locking/lockdep.c:5087
lock_acquire+0x19e/0x420 kernel/locking/lockdep.c:5754
fs_reclaim_acquire+0x98/0x100 mm/page_alloc.c:3617
might_alloc include/linux/sched/mm.h:303 [inline]
prepare_alloc_pages+0x156/0x5b0 mm/page_alloc.c:4271
__alloc_pages+0x134/0x460 mm/page_alloc.c:4490
__folio_alloc+0x10/0x20 mm/page_alloc.c:4533
vma_alloc_folio+0x474/0x8f0 mm/mempolicy.c:2240
shmem_alloc_folio+0x1a9/0x2a0 mm/shmem.c:1679
shmem_alloc_and_acct_folio+0x1cb/0x6c0 mm/shmem.c:1704
shmem_get_folio_gfp+0xe1d/0x2b40 mm/shmem.c:2041
shmem_get_folio mm/shmem.c:2164 [inline]
shmem_write_begin+0xf2/0x430 mm/shmem.c:2706
generic_perform_write+0x2fe/0x5c0 mm/filemap.c:4036
shmem_file_write_iter+0xfb/0x120 mm/shmem.c:2883
__kernel_write_iter+0x29f/0x6d0 fs/read_write.c:517
dump_emit_page fs/coredump.c:958 [inline]
dump_user_range+0x418/0x840 fs/coredump.c:985
elf_core_dump+0x320e/0x37c0 fs/binfmt_elf.c:2184
do_coredump+0x1791/0x24a0 fs/coredump.c:834
get_signal+0x10da/0x1390 kernel/signal.c:2897
arch_do_signal_or_restart+0xc2/0x7b0 arch/x86/kernel/signal.c:310
exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:174
exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:210
irqentry_exit_to_user_mode+0x9/0x30 kernel/entry/common.c:315
exc_page_fault+0x8c/0x100 arch/x86/mm/fault.c:1519
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:608
RIP: 0033:0x7f25d219e0e1
Code: 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 83 c8 ff c3 66 2e 0f 1f
RSP: 002b:fffffffffffffe70 EFLAGS: 00010217
RAX: 0000000000000000 RBX: 00007f25d2425fa0 RCX: 00007f25d219e0d9
RDX: 0000000000000000 RSI: fffffffffffffe70 RDI: 0000000000008000
RBP: 00007f25d2235024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 00007f25d2426038 R14: 00007f25d2425fa0 R15: 00007fff26fb0068
</TASK>
Struck through repros no longer work on HEAD.