Re: [syzbot] [lsm] [kernel] INFO: task hung in restrict_one_thread_callback

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
INFO: task hung in restrict_one_thread_callback

INFO: task syz.0.140:6853 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.140       state:D stack:25600 pid:6853  tgid:6853  ppid:6361   task_flags:0x400040 flags:0x00080002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5295 [inline]
 __schedule+0x1585/0x5340 kernel/sched/core.c:6907
 __schedule_loop kernel/sched/core.c:6989 [inline]
 schedule+0x164/0x360 kernel/sched/core.c:7004
 schedule_timeout+0xc3/0x2c0 kernel/time/sleep_timeout.c:75
 do_wait_for_common kernel/sched/completion.c:100 [inline]
 __wait_for_common kernel/sched/completion.c:121 [inline]
 wait_for_common kernel/sched/completion.c:132 [inline]
 wait_for_completion+0x2cc/0x5e0 kernel/sched/completion.c:153
 restrict_one_thread security/landlock/tsync.c:128 [inline]
 restrict_one_thread_callback+0x320/0x570 security/landlock/tsync.c:162
 task_work_run+0x1d9/0x270 kernel/task_work.c:233
 get_signal+0x11eb/0x1330 kernel/signal.c:2807
 arch_do_signal_or_restart+0xbc/0x830 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:64 [inline]
 exit_to_user_mode_loop+0x86/0x480 kernel/entry/common.c:98
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline]
 do_syscall_64+0x32d/0xf80 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2c1c79bf79
RSP: 002b:00007ffccde0b128 EFLAGS: 00000246 ORIG_RAX: 00000000000000db
RAX: fffffffffffffdfc RBX: 000000000001f230 RCX: 00007f2c1c79bf79
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007f2c1ca1618c
RBP: 0000000000000032 R08: 3fffffffffffffff R09: 0000000000000000
R10: 00007ffccde0b230 R11: 0000000000000246 R12: 00007ffccde0b250
R13: 00007f2c1ca1618c R14: 000000000001f262 R15: 00007ffccde0b230
 </TASK>
INFO: task syz.0.140:6854 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.140       state:D stack:28264 pid:6854  tgid:6853  ppid:6361   task_flags:0x400040 flags:0x00080002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5295 [inline]
 __schedule+0x1585/0x5340 kernel/sched/core.c:6907
 __schedule_loop kernel/sched/core.c:6989 [inline]
 schedule+0x164/0x360 kernel/sched/core.c:7004
 schedule_timeout+0xc3/0x2c0 kernel/time/sleep_timeout.c:75
 do_wait_for_common kernel/sched/completion.c:100 [inline]
 __wait_for_common kernel/sched/completion.c:121 [inline]
 wait_for_common kernel/sched/completion.c:132 [inline]
 wait_for_completion+0x2cc/0x5e0 kernel/sched/completion.c:153
 restrict_one_thread security/landlock/tsync.c:128 [inline]
 restrict_one_thread_callback+0x320/0x570 security/landlock/tsync.c:162
 task_work_run+0x1d9/0x270 kernel/task_work.c:233
 get_signal+0x11eb/0x1330 kernel/signal.c:2807
 arch_do_signal_or_restart+0xbc/0x830 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:64 [inline]
 exit_to_user_mode_loop+0x86/0x480 kernel/entry/common.c:98
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline]
 do_syscall_64+0x32d/0xf80 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2c1c79bf79
RSP: 002b:00007f2c1d6710e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00007f2c1ca15fa8 RCX: 00007f2c1c79bf79
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007f2c1ca15fa8
RBP: 00007f2c1ca15fa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2c1ca16038 R14: 00007ffccde0aee0 R15: 00007ffccde0afc8
 </TASK>
INFO: task syz.0.140:6855 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.140       state:D stack:28216 pid:6855  tgid:6853  ppid:6361   task_flags:0x400140 flags:0x00080006
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5295 [inline]
 __schedule+0x1585/0x5340 kernel/sched/core.c:6907
 __schedule_loop kernel/sched/core.c:6989 [inline]
 schedule+0x164/0x360 kernel/sched/core.c:7004
 schedule_timeout+0xc3/0x2c0 kernel/time/sleep_timeout.c:75
 do_wait_for_common kernel/sched/completion.c:100 [inline]
 __wait_for_common kernel/sched/completion.c:121 [inline]
 wait_for_common kernel/sched/completion.c:132 [inline]
 wait_for_completion+0x2cc/0x5e0 kernel/sched/completion.c:153
 landlock_restrict_sibling_threads+0xe9c/0x11f0 security/landlock/tsync.c:539
 __do_sys_landlock_restrict_self security/landlock/syscalls.c:574 [inline]
 __se_sys_landlock_restrict_self+0x540/0x810 security/landlock/syscalls.c:482
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2c1c79bf79
RSP: 002b:00007f2c1d650028 EFLAGS: 00000246 ORIG_RAX: 00000000000001be
RAX: ffffffffffffffda RBX: 00007f2c1ca16090 RCX: 00007f2c1c79bf79
RDX: 0000000000000000 RSI: 000000000000000e RDI: 0000000000000003
RBP: 00007f2c1c8327e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2c1ca16128 R14: 00007f2c1ca16090 R15: 00007ffccde0afc8
 </TASK>
INFO: task syz.0.140:6856 blocked for more than 144 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.140       state:D stack:28368 pid:6856  tgid:6853  ppid:6361   task_flags:0x400140 flags:0x00080006
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5295 [inline]
 __schedule+0x1585/0x5340 kernel/sched/core.c:6907
 __schedule_loop kernel/sched/core.c:6989 [inline]
 schedule+0x164/0x360 kernel/sched/core.c:7004
 schedule_timeout+0xc3/0x2c0 kernel/time/sleep_timeout.c:75
 do_wait_for_common kernel/sched/completion.c:100 [inline]
 __wait_for_common kernel/sched/completion.c:121 [inline]
 wait_for_common kernel/sched/completion.c:132 [inline]
 wait_for_completion+0x2cc/0x5e0 kernel/sched/completion.c:153
 landlock_restrict_sibling_threads+0xe9c/0x11f0 security/landlock/tsync.c:539
 __do_sys_landlock_restrict_self security/landlock/syscalls.c:574 [inline]
 __se_sys_landlock_restrict_self+0x540/0x810 security/landlock/syscalls.c:482
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2c1c79bf79
RSP: 002b:00007f2c1d62f028 EFLAGS: 00000246 ORIG_RAX: 00000000000001be
RAX: ffffffffffffffda RBX: 00007f2c1ca16180 RCX: 00007f2c1c79bf79
RDX: 0000000000000000 RSI: 000000000000000e RDI: 0000000000000003
RBP: 00007f2c1c8327e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2c1ca16218 R14: 00007f2c1ca16180 R15: 00007ffccde0afc8
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/31:
 #0: ffffffff8e9602e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:312 [inline]
 #0: ffffffff8e9602e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:850 [inline]
 #0: ffffffff8e9602e0 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 kernel/locking/lockdep.c:6775
5 locks held by kworker/u8:10/1152:
 #0: ffff8880b873ade0 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x31/0x150 kernel/sched/core.c:647
 #1: ffff8880b8724588 (psi_seq){-.-.}-{0:0}, at: psi_task_switch+0x53/0x880 kernel/sched/psi.c:933
 #2: ffff888053c88788 (&rdev->wiphy.mtx){+.+.}-{4:4}, at: class_wiphy_constructor include/net/cfg80211.h:6441 [inline]
 #2: ffff888053c88788 (&rdev->wiphy.mtx){+.+.}-{4:4}, at: cfg80211_wiphy_work+0xb4/0x4a0 net/wireless/core.c:426
 #3: ffffffff8e9602e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:312 [inline]
 #3: ffffffff8e9602e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:850 [inline]
 #3: ffffffff8e9602e0 (rcu_read_lock){....}-{1:3}, at: ieee80211_sta_active_ibss+0xc3/0x330 net/mac80211/ibss.c:635
 #4: ffffffff8e9602e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:312 [inline]
 #4: ffffffff8e9602e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:850 [inline]
 #4: ffffffff8e9602e0 (rcu_read_lock){....}-{1:3}, at: class_rcu_constructor include/linux/rcupdate.h:1193 [inline]
 #4: ffffffff8e9602e0 (rcu_read_lock){....}-{1:3}, at: unwind_next_frame+0xa5/0x23c0 arch/x86/kernel/unwind_orc.c:495
2 locks held by getty/5584:
 #0: ffff888037fb00a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
 #1: ffffc9000332b2f0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x45c/0x13c0 drivers/tty/n_tty.c:2211

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

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 02/12/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 nmi_cpu_backtrace+0x274/0x2d0 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x17a/0x300 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:161 [inline]
 __sys_info lib/sys_info.c:157 [inline]
 sys_info+0x135/0x170 lib/sys_info.c:165
 check_hung_uninterruptible_tasks kernel/hung_task.c:346 [inline]
 watchdog+0xfd9/0x1030 kernel/hung_task.c:515
 kthread+0x388/0x470 kernel/kthread.c:467
 ret_from_fork+0x51e/0xb90 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: 13992 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:rcu_read_unlock include/linux/rcupdate.h:879 [inline]
RIP: 0010:xa_load+0x16a/0x210 lib/xarray.c:1621
Code: 06 04 00 00 75 07 e8 f5 4e 0f f6 eb c3 e8 6e bb 01 00 89 c5 31 ff 89 c6 e8 23 53 0f f6 85 ed 74 10 e8 9a 68 f4 f5 84 c0 74 0e <e8> d1 4e 0f f6 eb 56 e8 ca 4e 0f f6 eb 4f e8 43 bb 01 00 89 c5 31
RSP: 0018:ffffc90003497230 EFLAGS: 00000202
RAX: 0000000000000001 RBX: ffffffff8bb68ba0 RCX: 0000000080000001
RDX: ffff8880584c3c80 RSI: ffffffff8c29ba60 RDI: ffffffff8c29ba20
RBP: 0000000000000001 R08: ffff8880584c3c80 R09: 0000000000000002
R10: 0000000000000406 R11: 0000000000000000 R12: 0000000000000000
R13: dffffc0000000000 R14: ffff88803369ca00 R15: ffffc90003497230
FS:  000055558749a500(0000) GS:ffff888125311000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f92f6facc00 CR3: 0000000074826000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 memcg_list_lru_allocated mm/list_lru.c:510 [inline]
 memcg_list_lru_alloc+0x14c/0x800 mm/list_lru.c:521
 __memcg_slab_post_alloc_hook+0x312/0xa80 mm/memcontrol.c:3220
 memcg_slab_post_alloc_hook mm/slub.c:2459 [inline]
 slab_post_alloc_hook mm/slub.c:4512 [inline]
 slab_alloc_node mm/slub.c:4830 [inline]
 kmem_cache_alloc_lru_noprof+0x346/0x640 mm/slub.c:4849
 __d_alloc+0x37/0x6f0 fs/dcache.c:1740
 d_alloc_parallel+0xe6/0x1610 fs/dcache.c:2604
 __lookup_slow+0x137/0x410 fs/namei.c:1901
 lookup_slow+0x53/0x70 fs/namei.c:1933
 walk_component fs/namei.c:2279 [inline]
 link_path_walk+0x1273/0x18d0 fs/namei.c:2644
 path_openat+0x2c3/0x3860 fs/namei.c:4826
 do_file_open+0x23e/0x4a0 fs/namei.c:4859
 do_sys_openat2+0x113/0x200 fs/open.c:1366
 do_sys_open fs/open.c:1372 [inline]
 __do_sys_openat fs/open.c:1388 [inline]
 __se_sys_openat fs/open.c:1383 [inline]
 __x64_sys_openat+0x138/0x170 fs/open.c:1383
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f92f6f5c84e
Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
RSP: 002b:00007ffcaf09ae38 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 000055558749a500 RCX: 00007f92f6f5c84e
RDX: 0000000000080001 RSI: 00007f92f703376c RDI: ffffffffffffff9c
RBP: 00007f92f703376c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000004
R13: 00007ffcaf09af10 R14: 0000000000043e78 R15: 00007ffcaf09b480
 </TASK>


Tested on:

commit:         7dff99b3 Remove WARN_ALL_UNSEEDED_RANDOM kernel config..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16d4f152580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=56c0294cb1688557
dashboard link: https://syzkaller.appspot.com/bug?extid=7ea2f5e9dfd468201817
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

Note: no patches were applied.