syzbot

INFO: task syz.1.18:5922 blocked for more than 143 seconds.
      Not tainte[  368.225405][   T39]       Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.1.18        state:D stack:28360 pid:5922  tgid:5920  ppid:5886   task_flags:0x400140 flags:0x00080002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5510 [inline]
 __schedule+0x1709/0x5530 kernel/sched/core.c:7231
 __schedule_loop kernel/sched/core.c:7308 [inline]
 schedule+0x164/0x2b0 kernel/sched/core.c:7323
 cgroup_lock_and_drain_offline+0x51a/0x650 kernel/cgroup/cgroup.c:3275
 cgroup_kn_lock_live+0x120/0x230 kernel/cgroup/cgroup.c:1715
 cgroup_subtree_control_write+0x4b5/0x1080 kernel/cgroup/cgroup.c:3577
 cgroup_file_write+0x331/0x8f0 kernel/cgroup/cgroup.c:4316
 kernfs_fop_write_iter+0x3a5/0x540 fs/kernfs/file.c:345
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x61e/0xbb0 fs/read_write.c:687
 ksys_write+0x156/0x270 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x17b/0x530 arch/x86/entry/syscall_64.c:85
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f1147d5de99
RSP: 002b:00007f114739d028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f1147fe6090 RCX: 00007f1147d5de99
RDX: 0000000000000005 RSI: 0000200000000040 RDI: 0000000000000007
RBP: 00007f1147df3eaf R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1147fe6128 R14: 00007f1147fe6090 R15: 00007ffd6d790368
 </TASK>

Showing all locks held in the system:
locks held by khungtaskd/39: 1, last CPU#1:
 #0: ffffffff8e3c3880 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #0: ffffffff8e3c3880 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
 #0: ffffffff8e3c3880 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 kernel/locking/lockdep.c:6835
locks held by kworker/0:2/823: 3, on CPU#0:
 #0: ffff88813fe63938 ((wq_completion)events){+.+.}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #0: ffff88813fe63938 ((wq_completion)events){+.+.}-{0:0}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
 #0: ffff88813fe63938 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x7fd/0x1480 kernel/workqueue.c:3344
 #1: ffffc90005577c60 ((work_completion)(&data->fib_event_work)){+.+.}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #1: ffffc90005577c60 ((work_completion)(&data->fib_event_work)){+.+.}-{0:0}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
 #1: ffffc90005577c60 ((work_completion)(&data->fib_event_work)){+.+.}-{0:0}, at: process_one_work+0x7fd/0x1480 kernel/workqueue.c:3344
 #2: ffff88803f7e5280 (&data->fib_lock){+.+.}-{4:4}, at: nsim_fib_event_work+0x222/0x3e0 drivers/net/netdevsim/fib.c:1490
locks held by kworker/u8:9/1178: 2, last CPU#0:
 #0: ffff8880326ac938 ((wq_completion)bat_events){+.+.}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #0: ffff8880326ac938 ((wq_completion)bat_events){+.+.}-{0:0}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
 #0: ffff8880326ac938 ((wq_completion)bat_events){+.+.}-{0:0}, at: process_one_work+0x7fd/0x1480 kernel/workqueue.c:3344
 #1: ffffc90006687c60 ((work_completion)(&(&bat_priv->tt.work)->work)){+.+.}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #1: ffffc90006687c60 ((work_completion)(&(&bat_priv->tt.work)->work)){+.+.}-{0:0}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
 #1: ffffc90006687c60 ((work_completion)(&(&bat_priv->tt.work)->work)){+.+.}-{0:0}, at: process_one_work+0x7fd/0x1480 kernel/workqueue.c:3344
locks held by getty/5348: 2, on CPU#1:
 #0: ffff88823bf2e0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
 #1: ffffc900044ce2e0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x460/0x1360 drivers/tty/n_tty.c:2211
locks held by syz.1.18/5922: 3, on CPU#1:
 #0: ffff88803c5d0928 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1259
 #1: ffff88804011a510 (sb_writers#9){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2731 [inline]
 #1: ffff88804011a510 (sb_writers#9){.+.+}-{0:0}, at: vfs_write+0x231/0xbb0 fs/read_write.c:683
 #2: ffff88803d939c78 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x1d9/0x540 fs/kernfs/file.c:336
locks held by syz.2.19/5964: 3, on CPU#0:
 #0: ffff88803b809528 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1259
 #1: ffff88804011a510 (sb_writers#9){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2731 [inline]
 #1: ffff88804011a510 (sb_writers#9){.+.+}-{0:0}, at: vfs_write+0x231/0xbb0 fs/read_write.c:683
 #2: ffff88804423b878 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x1d9/0x540 fs/kernfs/file.c:336
locks held by syz.2.19/5965: 1, on CPU#1:
 #0: ffff88803b809528 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1259
locks held by syz.3.20/6007: 3, on CPU#1:
 #0: ffff8880331b9128 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1259
 #1: ffff88804011a510 (sb_writers#9){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2731 [inline]
 #1: ffff88804011a510 (sb_writers#9){.+.+}-{0:0}, at: vfs_write+0x231/0xbb0 fs/read_write.c:683
 #2: ffff888035000c78 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x1d9/0x540 fs/kernfs/file.c:336
locks held by syz.3.20/6008: 1, on CPU#0:
 #0: ffff8880331b9128 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1259
locks held by syz.4.21/6052: 3, on CPU#1:
 #0: ffff888038397f28 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1259
 #1: ffff88804011a510 (sb_writers#9){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2731 [inline]
 #1: ffff88804011a510 (sb_writers#9){.+.+}-{0:0}, at: vfs_write+0x231/0xbb0 fs/read_write.c:683
 #2: ffff888032e3a078 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x1d9/0x540 fs/kernfs/file.c:336
locks held by syz.4.21/6053: 1, on CPU#1:
 #0: ffff888038397f28 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1259
locks held by syz.5.22/6097: 3, on CPU#0:
 #0: ffff888025eee328 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1259
 #1: ffff88804011a510 (sb_writers#9){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2731 [inline]
 #1: ffff88804011a510 (sb_writers#9){.+.+}-{0:0}, at: vfs_write+0x231/0xbb0 fs/read_write.c:683
 #2: ffff888036bc1078 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x1d9/0x540 fs/kernfs/file.c:336
locks held by syz.5.22/6098: 1, on CPU#1:
 #0: ffff888025eee328 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1259
locks held by syz.6.23/6148: 3, on CPU#0:
 #0: ffff88803566f128 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1259
 #1: ffff88804011a510 (sb_writers#9){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2731 [inline]
 #1: ffff88804011a510 (sb_writers#9){.+.+}-{0:0}, at: vfs_write+0x231/0xbb0 fs/read_write.c:683
 #2: ffff888038432078 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x1d9/0x540 fs/kernfs/file.c:336
locks held by syz.6.23/6149: 1, on CPU#0:
 #0: ffff88803566f128 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1259
locks held by syz.7.24/6197: 3, on CPU#0:
 #0: ffff88803833ed28 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1259
 #1: ffff88804011a510 (sb_writers#9){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2731 [inline]
 #1: ffff88804011a510 (sb_writers#9){.+.+}-{0:0}, at: vfs_write+0x231/0xbb0 fs/read_write.c:683
 #2: ffff88803ec1f078 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x1d9/0x540 fs/kernfs/file.c:336
locks held by syz.7.24/6198: 1, on CPU#1:
 #0: ffff88803833ed28 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1259
locks held by syz.8.25/6242: 3, on CPU#0:
 #0: ffff88803c5d6b28 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1259
 #1: ffff88804011a510 (sb_writers#9){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2731 [inline]
 #1: ffff88804011a510 (sb_writers#9){.+.+}-{0:0}, at: vfs_write+0x231/0xbb0 fs/read_write.c:683
 #2: ffff888044b62c78 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x1d9/0x540 fs/kernfs/file.c:336
locks held by syz.8.25/6243: 1, on CPU#1:
 #0: ffff88803c5d6b28 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x252/0x320 fs/file.c:1259
locks held by syz-executor/6246: 1, last CPU#1:
 #0: ffff88804578a478 (&sb->s_type->i_mutex_key#12){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:1024 [inline]
 #0: ffff88804578a478 (&sb->s_type->i_mutex_key#12){+.+.}-{4:4}, at: __sock_release+0x7a/0x1f0 net/socket.c:738

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

NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 39 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/25/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 nmi_cpu_backtrace+0x274/0x2d0 lib/nmi_backtrace.c:122
 nmi_trigger_cpumask_backtrace+0x17a/0x380 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+0x135/0x170 lib/sys_info.c:165
 check_hung_uninterruptible_tasks kernel/hung_task.c:353 [inline]
 watchdog+0xfd7/0x1030 kernel/hung_task.c:561
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 74 Comm: kworker/u8:6 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/25/2026
Workqueue: ipv6_addrconf addrconf_dad_work
RIP: 0010:__bfs kernel/locking/lockdep.c:-1 [inline]
RIP: 0010:__bfs_backwards kernel/locking/lockdep.c:1876 [inline]
RIP: 0010:check_irq_usage kernel/locking/lockdep.c:2812 [inline]
RIP: 0010:check_prev_add kernel/locking/lockdep.c:3185 [inline]
RIP: 0010:check_prevs_add kernel/locking/lockdep.c:3300 [inline]
RIP: 0010:validate_chain kernel/locking/lockdep.c:3924 [inline]
RIP: 0010:__lock_acquire+0x19f2/0x2e40 kernel/locking/lockdep.c:5254
Code: 00 39 05 ed 7e 27 12 73 06 89 05 e5 7e 27 12 48 8b 02 49 89 d8 4c 39 e8 0f 84 30 fe ff ff 4c 89 78 30 48 8b 00 4c 39 e8 75 f4 <49> 89 d8 e9 1c fe ff ff 48 c7 c7 30 0b 29 8e 4c 89 e6 4c 89 c3 e8
RSP: 0018:ffffc900015be310 EFLAGS: 00000046
RAX: ffffffff9372c450 RBX: 00000000000003cd RCX: 0000000000000259
RDX: ffffffff9668fe48 RSI: ffff88801eb04ca0 RDI: ffff88801eb03e80
RBP: 9bbcbd8294ec9129 R08: 00000000000003cd R09: 0000000000000020
R10: 0000000000000000 R11: ffffffff81a16ef0 R12: 0000000000000258
R13: ffffffff9372c450 R14: ffff88801eb04ca0 R15: ffffffff96690858
FS:  0000000000000000(0000) GS:ffff8881259f2000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffc07a84f90 CR3: 000000000e1b0000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5906
 _raw_spin_lock_nested+0x32/0x50 kernel/locking/spinlock.c:382
 raw_spin_rq_lock_nested+0x2d/0x160 kernel/sched/core.c:667
 raw_spin_rq_lock kernel/sched/sched.h:1664 [inline]
 _task_rq_lock+0xc0/0x440 kernel/sched/core.c:762
 class_task_rq_lock_constructor kernel/sched/sched.h:1974 [inline]
 migrate_disable_switch kernel/sched/core.c:2464 [inline]
 __schedule+0x1888/0x5530 kernel/sched/core.c:7086
 preempt_schedule_irq+0x4d/0xa0 kernel/sched/core.c:7553
 irqentry_exit_to_kernel_mode include/linux/irq-entry-common.h:539 [inline]
 irqentry_exit+0x14f/0x8f0 kernel/entry/common.c:167
 asm_sysvec_reschedule_ipi+0x1a/0x20 arch/x86/include/asm/idtentry.h:679
RIP: 0010:save_dst_trace_buffer+0x1f1/0x5b0 net/core/dst.c:104
Code: 74 73 e8 92 22 9c f8 48 8b 1c 24 48 81 fb 40 ff 17 00 74 2d e8 80 22 9c f8 48 81 c3 c0 00 00 00 49 83 c6 18 48 83 44 24 30 e8 <48> 83 44 24 28 e8 49 83 c5 e8 49 83 c7 e8 49 83 c4 e8 e9 72 ff ff
RSP: 0018:ffffc900015be8c0 EFLAGS: 00000297
RAX: ffffffff89298130 RBX: 0000000000006480 RCX: ffff88801eb03e80
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc900015bea58 R08: 0000000000000000 R09: 0000000000000000
R10: ffffc900015be820 R11: fffff520002b7d08 R12: e00000000caf2d5b
R13: e00000000caf2d5a R14: 1ffffffff350d2bc R15: e00000000caf2d5a
 dst_release+0x28/0x1b0 net/core/dst.c:250
 refdst_drop include/net/dst.h:286 [inline]
 skb_dst_drop include/net/dst.h:298 [inline]
 __dev_queue_xmit+0x4c6/0x3880 net/core/dev.c:4829
 dev_queue_xmit include/linux/netdevice.h:3457 [inline]
 br_dev_queue_push_xmit+0x370/0x4b0 net/bridge/br_forward.c:53
 NF_HOOK+0x360/0x3f0 include/linux/netfilter.h:325
 br_forward_finish+0xd3/0x130 net/bridge/br_forward.c:66
 NF_HOOK+0x360/0x3f0 include/linux/netfilter.h:325
 __br_forward+0x397/0x540 net/bridge/br_forward.c:115
 br_dev_xmit+0x1235/0x1a30 net/bridge/br_device.c:108
 __netdev_start_xmit include/linux/netdevice.h:5439 [inline]
 netdev_start_xmit include/linux/netdevice.h:5448 [inline]
 xmit_one net/core/dev.c:3893 [inline]
 dev_hard_start_xmit+0x2df/0x870 net/core/dev.c:3909
 __dev_queue_xmit+0x14d2/0x3880 net/core/dev.c:4882
 NF_HOOK_COND include/linux/netfilter.h:314 [inline]
 ip6_output+0x337/0x540 net/ipv6/ip6_output.c:246
 dst_output include/net/dst.h:489 [inline]
 NF_HOOK+0x177/0x4f0 include/linux/netfilter.h:325
 mld_sendpack+0x890/0xe10 net/ipv6/mcast.c:1870
 ipv6_mc_dad_complete+0x87/0x410 net/ipv6/mcast.c:2296
 addrconf_dad_completed+0x622/0xe60 net/ipv6/addrconf.c:4375
 addrconf_dad_work+0xdda/0x16e0 net/ipv6/addrconf.c:-1
 process_one_work+0xaaf/0x1480 kernel/workqueue.c:3379
 process_scheduled_works kernel/workqueue.c:3462 [inline]
 worker_thread+0xb05/0x10d0 kernel/workqueue.c:3543
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>