syzbot

INFO: task syz.4.4370:13148 blocked for more than 122 seconds.
      Not tainted 6.12.23-syzkaller-gd9fd901baa98 #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.4.4370      state:D stack:0     pid:13148 tgid:13146 ppid:11620  flags:0x00004006
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5924 [inline]
 __schedule+0x145b/0x1f10 kernel/sched/core.c:7750
 __schedule_loop kernel/sched/core.c:7831 [inline]
 schedule+0xc6/0x240 kernel/sched/core.c:7846
 request_wait_answer fs/fuse/dev.c:472 [inline]
 __fuse_request_send fs/fuse/dev.c:487 [inline]
 __fuse_simple_request+0xdac/0x1970 fs/fuse/dev.c:582
 fuse_simple_request fs/fuse/fuse_i.h:1248 [inline]
 fuse_flush+0x909/0x1d50 fs/fuse/file.c:582
 filp_flush fs/open.c:1550 [inline]
 filp_close+0xbd/0x160 fs/open.c:1563
 close_files fs/file.c:419 [inline]
 put_files_struct+0x1b5/0x330 fs/file.c:434
 exit_files+0x84/0xa0 fs/file.c:451
 do_exit+0x97d/0x2630 kernel/exit.c:939
 do_group_exit+0x22a/0x300 kernel/exit.c:1094
 get_signal+0x139d/0x14f0 kernel/signal.c:2934
 arch_do_signal_or_restart+0x96/0x720 arch/x86/kernel/signal.c:337
 exit_to_user_mode_loop kernel/entry/common.c:111 [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+0x58/0xb0 kernel/entry/common.c:218
 do_syscall_64+0x64/0xf0 arch/x86/entry/common.c:89
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7fc167b8e929
RSP: 002b:00007fc16899e0e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00007fc167db6088 RCX: 00007fc167b8e929
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007fc167db6088
RBP: 00007fc167db6080 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fc167db608c
R13: 0000000000000000 R14: 00007ffdcab0b780 R15: 00007ffdcab0b868
 </TASK>
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 37 Comm: khungtaskd Not tainted 6.12.23-syzkaller-gd9fd901baa98 #0 f1acc3ef52b3e732a05c4f7a2560722db90bb473
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 __dump_stack+0x21/0x30 lib/dump_stack.c:94
 dump_stack_lvl+0x10c/0x190 lib/dump_stack.c:120
 dump_stack+0x19/0x20 lib/dump_stack.c:129
 nmi_cpu_backtrace+0x2bf/0x2d0 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x142/0x2c0 lib/nmi_backtrace.c:62
 arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:41
 trigger_all_cpu_backtrace include/linux/nmi.h:158 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:229 [inline]
 watchdog+0xd8f/0xed0 kernel/hung_task.c:385
 kthread+0x2c7/0x370 kernel/kthread.c:389
 ret_from_fork+0x64/0xa0 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 17451 Comm: syz.9.5758 Not tainted 6.12.23-syzkaller-gd9fd901baa98 #0 f1acc3ef52b3e732a05c4f7a2560722db90bb473
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:io_serial_out+0x85/0xd0 drivers/tty/serial/8250/8250_port.c:413
Code: fe 44 89 e1 41 d3 e6 49 83 c7 08 4c 89 f8 48 c1 e8 03 42 80 3c 28 00 74 08 4c 89 ff e8 84 4f c4 fe 45 03 37 89 d8 44 89 f2 ee <5b> 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc cc 44 89 e1 80 e1 07
RSP: 0018:ffffc90002cee4c8 EFLAGS: 00000006
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 00000000000003f9 RSI: 000000000007ffff RDI: 0000000000080000
RBP: ffffc90002cee4f0 R08: 0000000000000003 R09: 0000000000000004
R10: 0000000000000000 R11: ffffffff831717d0 R12: 0000000000000000
R13: dffffc0000000000 R14: 00000000000003f9 R15: ffffffff889d6d08
FS:  00007ff302bf96c0(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fecc8381178 CR3: 000000011688a000 CR4: 00000000003526b0
DR0: 000000000000634b DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 serial_out drivers/tty/serial/8250/8250.h:142 [inline]
 serial8250_clear_IER drivers/tty/serial/8250/8250_port.c:-1 [inline]
 serial8250_console_write+0x3a6/0x2130 drivers/tty/serial/8250/8250_port.c:3387
 univ8250_console_write+0x6f/0xb0 drivers/tty/serial/8250/8250_core.c:396
 console_emit_next_record kernel/printk/printk.c:3134 [inline]
 console_flush_all+0x5e3/0xaa0 kernel/printk/printk.c:3222
 __console_flush_and_unlock kernel/printk/printk.c:3281 [inline]
 console_unlock+0xe9/0x270 kernel/printk/printk.c:3321
 vprintk_emit+0x27c/0x640 kernel/printk/printk.c:2443
 vprintk_default+0x2a/0x40 kernel/printk/printk.c:2458
 vprintk+0x93/0xa0 kernel/printk/printk_safe.c:73
 _printk+0xd0/0x120 kernel/printk/printk.c:2468
 __netdev_printk+0x3b6/0x4e0 net/core/dev.c:11903
 netdev_info+0x10b/0x160 net/core/dev.c:11950
 tun_net_xmit+0x779/0x1280 drivers/net/tun.c:1087
 __netdev_start_xmit include/linux/netdevice.h:4975 [inline]
 netdev_start_xmit include/linux/netdevice.h:4984 [inline]
 xmit_one net/core/dev.c:3662 [inline]
 dev_hard_start_xmit+0x218/0x770 net/core/dev.c:3678
 sch_direct_xmit+0x259/0x8f0 net/sched/sch_generic.c:343
 __dev_xmit_skb net/core/dev.c:3904 [inline]
 __dev_queue_xmit+0x16c3/0x3790 net/core/dev.c:4480
 dev_queue_xmit include/linux/netdevice.h:3141 [inline]
 neigh_hh_output include/net/neighbour.h:534 [inline]
 neigh_output include/net/neighbour.h:548 [inline]
 ip_finish_output2+0xbd7/0xf20 net/ipv4/ip_output.c:236
 __ip_finish_output+0x17b/0x3e0 net/ipv4/ip_output.c:-1
 ip_finish_output+0x35/0x360 net/ipv4/ip_output.c:324
 NF_HOOK_COND include/linux/netfilter.h:306 [inline]
 ip_output+0x160/0x2a0 net/ipv4/ip_output.c:434
 dst_output include/net/dst.h:459 [inline]
 ip_local_out net/ipv4/ip_output.c:130 [inline]
 ip_send_skb+0x173/0x1b0 net/ipv4/ip_output.c:1496
 udp_send_skb+0xa1b/0x1340 net/ipv4/udp.c:1041
 udp_sendmsg+0x1640/0x21f0 net/ipv4/udp.c:1335
 inet_sendmsg+0xef/0x120 net/ipv4/af_inet.c:858
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg net/socket.c:745 [inline]
 ____sys_sendmsg+0x82a/0xa70 net/socket.c:2610
 ___sys_sendmsg+0x220/0x2a0 net/socket.c:2664
 __sys_sendmmsg+0x271/0x470 net/socket.c:2750
 __do_sys_sendmmsg net/socket.c:2779 [inline]
 __se_sys_sendmmsg net/socket.c:2776 [inline]
 __x64_sys_sendmmsg+0xa4/0xc0 net/socket.c:2776
 x64_sys_call+0xfec/0x2ee0 arch/x86/include/generated/asm/syscalls_64.h:308
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x58/0xf0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7ff301d8e929
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ff302bf9038 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007ff301fb5fa0 RCX: 00007ff301d8e929
RDX: 000000000800001d RSI: 0000200000007fc0 RDI: 0000000000000008
RBP: 00007ff301e10b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007ff301fb5fa0 R15: 00007ffe055abe78
 </TASK>