syzbot

INFO: task syz.4.819:10135 blocked for more than 143 seconds.
      Tainted: G             L      syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.4.819       state:D stack:25208 pid:10135 tgid:10132 ppid:6323   task_flags:0x400140 flags:0x00080002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5388 [inline]
 __schedule+0x1295/0x67a0 kernel/sched/core.c:7189
 __schedule_loop kernel/sched/core.c:7268 [inline]
 schedule+0xdd/0x390 kernel/sched/core.c:7283
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7340
 __mutex_lock_common kernel/locking/mutex.c:726 [inline]
 __mutex_lock+0xced/0x1b10 kernel/locking/mutex.c:820
 nfsd_nl_version_get_doit+0x18c/0x7f0 fs/nfsd/nfsctl.c:1863
 genl_family_rcv_msg_doit+0x214/0x300 net/netlink/genetlink.c:1114
 genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
 genl_rcv_msg+0x560/0x800 net/netlink/genetlink.c:1209
 netlink_rcv_skb+0x159/0x420 net/netlink/af_netlink.c:2550
 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0x585/0x850 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x8b0/0xda0 net/netlink/af_netlink.c:1894
 sock_sendmsg_nosec net/socket.c:787 [inline]
 __sock_sendmsg net/socket.c:802 [inline]
 ____sys_sendmsg+0x9e1/0xb70 net/socket.c:2698
 ___sys_sendmsg+0x190/0x1e0 net/socket.c:2752
 __sys_sendmsg+0x170/0x220 net/socket.c:2784
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x10b/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f8eb5d9cdd9
RSP: 002b:00007f8eb6c2b028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f8eb6015fa0 RCX: 00007f8eb5d9cdd9
RDX: 0000000000008010 RSI: 0000200000000100 RDI: 0000000000000003
RBP: 00007f8eb5e32d69 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f8eb6016038 R14: 00007f8eb6015fa0 R15: 00007ffe36696668
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/31:
 #0: ffffffff8e7e52e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #0: ffffffff8e7e52e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
 #0: ffffffff8e7e52e0 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x3d/0x184 kernel/locking/lockdep.c:6775
3 locks held by kworker/0:3/5628:
 #0: ffff88813fe57140 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x12d6/0x1980 kernel/workqueue.c:3277
 #1: ffffc90003c6fd08 ((fqdir_free_work).work){+.+.}-{0:0}, at: process_one_work+0x973/0x1980 kernel/workqueue.c:3278
 #2: ffffffff8e7f0cf8 (rcu_state.barrier_mutex){+.+.}-{4:4}, at: rcu_barrier+0x48/0x6d0 kernel/rcu/tree.c:3828
1 lock held by syz.2.215/6877:
5 locks held by kworker/u8:16/7740:
 #0: ffff88801c6ae140 ((wq_completion)netns){+.+.}-{0:0}, at: process_one_work+0x12d6/0x1980 kernel/workqueue.c:3277
 #1: ffffc90004117d08 (net_cleanup_work){+.+.}-{0:0}, at: process_one_work+0x973/0x1980 kernel/workqueue.c:3278
 #2: ffffffff905f6368 (pernet_ops_rwsem){++++}-{4:4}, at: cleanup_net+0xb8/0x920 net/core/net_namespace.c:673
 #3: ffffffff9060f0a0 (rtnl_mutex){+.+.}-{4:4}, at: ops_exit_rtnl_list net/core/net_namespace.c:173 [inline]
 #3: ffffffff9060f0a0 (rtnl_mutex){+.+.}-{4:4}, at: ops_undo_list+0x7ec/0xab0 net/core/net_namespace.c:248
 #4: ffffffff8e7f0e28 (rcu_state.exp_mutex){+.+.}-{4:4}, at: exp_funnel_lock+0x27f/0x3c0 kernel/rcu/tree_exp.h:311
2 locks held by syz.5.774/9868:
 #0: ffffffff906bd588 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1217
 #1: ffffffff8ec61b20 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_nl_listener_set_doit+0xd5/0x1a80 fs/nfsd/nfsctl.c:1938
2 locks held by syz.4.819/10135:
 #0: ffffffff906bd588 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1217
 #1: ffffffff8ec61b20 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_nl_version_get_doit+0x18c/0x7f0 fs/nfsd/nfsctl.c:1863
2 locks held by syz.8.1099/11541:
 #0: ffff888035ecc0d8 (&type->s_umount_key#53){+.+.}-{4:4}, at: __super_lock fs/super.c:58 [inline]
 #0: ffff888035ecc0d8 (&type->s_umount_key#53){+.+.}-{4:4}, at: __super_lock_excl fs/super.c:73 [inline]
 #0: ffff888035ecc0d8 (&type->s_umount_key#53){+.+.}-{4:4}, at: deactivate_super fs/super.c:508 [inline]
 #0: ffff888035ecc0d8 (&type->s_umount_key#53){+.+.}-{4:4}, at: deactivate_super+0xdf/0x110 fs/super.c:505
 #1: ffffffff8ec61b20 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
3 locks held by syz.7.1158/11816:
 #0: ffffffff906bd588 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1217
 #1: ffff8880585c86e8 (nlk_cb_mutex-GENERIC){+.+.}-{4:4}, at: __netlink_dump_start+0x150/0x990 net/netlink/af_netlink.c:2404
 #2: ffffffff8ec61b20 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_nl_rpc_status_get_dumpit+0xb7/0x1200 fs/nfsd/nfsctl.c:1494
2 locks held by syz.6.1181/11945:
3 locks held by syz.6.1181/11946:
2 locks held by syz.6.1181/11947:
2 locks held by syz.6.1181/11948:
2 locks held by syz.6.1181/11949:
2 locks held by syz.6.1181/11951:
3 locks held by syz.6.1181/11954:
1 lock held by syz.6.1181/11955:
3 locks held by syz.6.1181/11957:
2 locks held by syz.6.1181/11959:
2 locks held by syz.6.1181/11967:
2 locks held by syz.9.1229/12356:
 #0: ffffffff906bd588 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1217
 #1: ffffffff8ec61b20 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_nl_version_set_doit+0xc4/0x7a0 fs/nfsd/nfsctl.c:1788
1 lock held by syz.6.1227/12388:
 #0: ffff88807bd6c078 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:554 [inline]
 #0: ffff88807bd6c078 (&mm->mmap_lock){++++}-{4:4}, at: vm_mmap_pgoff+0x1f5/0x470 mm/util.c:579
1 lock held by syz.6.1227/12390:
 #0: ffff88807bd6c078 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_lock_killable include/linux/mmap_lock.h:601 [inline]
 #0: ffff88807bd6c078 (&mm->mmap_lock){++++}-{4:4}, at: get_mmap_lock_carefully mm/mmap_lock.c:450 [inline]
 #0: ffff88807bd6c078 (&mm->mmap_lock){++++}-{4:4}, at: lock_mm_and_find_vma+0x160/0x6f0 mm/mmap_lock.c:501
1 lock held by syz.6.1227/12391:
 #0: ffff88807bd6c078 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_lock_killable include/linux/mmap_lock.h:601 [inline]
 #0: ffff88807bd6c078 (&mm->mmap_lock){++++}-{4:4}, at: get_mmap_lock_carefully mm/mmap_lock.c:450 [inline]
 #0: ffff88807bd6c078 (&mm->mmap_lock){++++}-{4:4}, at: lock_mm_and_find_vma+0x160/0x6f0 mm/mmap_lock.c:501
1 lock held by syz.6.1227/12405:

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

NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 31 Comm: khungtaskd Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
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:113
 nmi_trigger_cpumask_backtrace+0x1d7/0x230 lib/nmi_backtrace.c:62
 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 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
RIP: 0010:io_serial_in+0x87/0xb0 drivers/tty/serial/8250/8250_port.c:402
Code: eb 8b fc 48 8d 7d 40 44 89 e1 48 b8 00 00 00 00 00 fc ff df 48 89 fa d3 e3 48 c1 ea 03 80 3c 02 00 75 1a 66 03 5d 40 89 da ec <5b> 0f b6 c0 5d 41 5c c3 cc cc cc cc e8 78 b3 f8 fc eb a2 e8 01 b4
RSP: 0018:ffffffff8e407810 EFLAGS: 00000002
RAX: dffffc0000000000 RBX: 00000000000003fd RCX: 0000000000000000
RDX: 00000000000003fd RSI: ffffffff857c1740 RDI: ffffffff9b462820
RBP: ffffffff9b4627e0 R08: 0000000000000001 R09: 000000000000001f
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000020 R14: fffffbfff368c556 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff888124377000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000000018b8 CR3: 000000000e596000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 serial_in drivers/tty/serial/8250/8250.h:128 [inline]
 serial_lsr_in drivers/tty/serial/8250/8250.h:150 [inline]
 wait_for_lsr+0x13a/0x210 drivers/tty/serial/8250/8250_port.c:1970
 serial8250_fifo_wait_for_lsr_thre drivers/tty/serial/8250/8250_port.c:3207 [inline]
 serial8250_console_fifo_write drivers/tty/serial/8250/8250_port.c:3272 [inline]
 serial8250_console_write+0xdb9/0x1900 drivers/tty/serial/8250/8250_port.c:3357
 console_emit_next_record kernel/printk/printk.c:3183 [inline]
 console_flush_one_record+0x790/0xe50 kernel/printk/printk.c:3269
 console_flush_all kernel/printk/printk.c:3343 [inline]
 __console_flush_and_unlock kernel/printk/printk.c:3373 [inline]
 console_unlock+0x103/0x260 kernel/printk/printk.c:3413
 vprintk_emit+0x407/0x6b0 kernel/printk/printk.c:2479
 _printk+0xcf/0x110 kernel/printk/printk.c:2504
 report_idle_softirq kernel/time/tick-sched.c:1204 [inline]
 can_stop_idle_tick.cold+0x13/0x1f kernel/time/tick-sched.c:1222
 tick_nohz_idle_stop_tick+0x799/0xeb0 kernel/time/tick-sched.c:1260
 idle_call_stop_or_retain_tick kernel/sched/idle.c:167 [inline]
 cpuidle_idle_call kernel/sched/idle.c:197 [inline]
 do_idle+0x45f/0x590 kernel/sched/idle.c:352
 cpu_startup_entry+0x4f/0x60 kernel/sched/idle.c:451
 rest_init+0x251/0x260 init/main.c:762
 start_kernel+0x484/0x490 init/main.c:1220
 x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:310
 x86_64_start_kernel+0x12b/0x130 arch/x86/kernel/head64.c:291
 common_startup_64+0x13e/0x148
 </TASK>