syzbot

INFO: task syz.9.729:2265 blocked for more than 122 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.9.729       state:D stack:0     pid:2265  tgid:2264  ppid:1823   flags:0x00000004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:6016 [inline]
 __schedule+0x134f/0x1ea0 kernel/sched/core.c:7864
 __schedule_loop kernel/sched/core.c:7945 [inline]
 schedule+0xc5/0x240 kernel/sched/core.c:7960
 schedule_timeout+0xc7/0x3b0 kernel/time/timer.c:2596
 down_write_failed drivers/tty/tty_ldsem.c:262 [inline]
 __ldsem_down_write_nested drivers/tty/tty_ldsem.c:324 [inline]
 ldsem_down_write+0x2a1/0x617 drivers/tty/tty_ldsem.c:366
 __tty_ldisc_lock drivers/tty/tty_ldisc.c:289 [inline]
 tty_ldisc_lock+0x6f/0xc0 drivers/tty/tty_ldisc.c:313
 tty_ldisc_hangup+0x25d/0x6e0 drivers/tty/tty_ldisc.c:718
 __tty_hangup+0x585/0x810 drivers/tty/tty_io.c:624
 tty_vhangup drivers/tty/tty_io.c:694 [inline]
 tty_ioctl+0x7c9/0xec0 drivers/tty/tty_io.c:2743
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0x135/0x1b0 fs/ioctl.c:893
 __x64_sys_ioctl+0x7f/0xa0 fs/ioctl.c:893
 x64_sys_call+0x1878/0x2ee0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/common.c:47 [inline]
 do_syscall_64+0x57/0xf0 arch/x86/entry/common.c:78
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7fb9e659c799
RSP: 002b:00007fb9e739a028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fb9e6815fa0 RCX: 00007fb9e659c799
RDX: 0000000000000002 RSI: 0000000000005437 RDI: 0000000000000005
RBP: 00007fb9e6632bd9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb9e6816038 R14: 00007fb9e6815fa0 R15: 00007ffcd95d2e08
 </TASK>
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 37 Comm: khungtaskd Not tainted syzkaller #0 3aad904d92044bb916fa84de8d678e40a290c0f4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 <TASK>
 __dump_stack+0x21/0x30 lib/dump_stack.c:94
 dump_stack_lvl+0x140/0x1c0 lib/dump_stack.c:120
 dump_stack+0x19/0x20 lib/dump_stack.c:129
 nmi_cpu_backtrace+0x2ba/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:267 [inline]
 watchdog+0xdad/0xf00 kernel/hung_task.c:423
 kthread+0x2c9/0x370 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 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 1480 Comm: syz.1.479 Not tainted syzkaller #0 3aad904d92044bb916fa84de8d678e40a290c0f4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:mutex_lock_interruptible+0x0/0x1d0 kernel/locking/mutex.c:1077
Code: df e9 01 ff ff ff e8 af 76 6a fb eb e5 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 b8 13 ca 9b c4 90 90 90 90 90 90 90 90 90 90 90 <f3> 0f 1e fa 55 48 89 e5 41 57 41 56 41 55 41 54 53 48 83 e4 e0 48
RSP: 0018:ffffc9001077fae8 EFLAGS: 00000246
RAX: ffffffff831bf454 RBX: 0000000000000000 RCX: 0000000000000002
RDX: ffff8881337d0000 RSI: 0000000000000000 RDI: ffff8881135f4060
RBP: ffffc9001077fb10 R08: ffff8881135f4067 R09: 1ffff110226be80c
R10: dffffc0000000000 R11: ffffed10226be80d R12: 0000000000000000
R13: dffffc0000000000 R14: ffff8881135f4060 R15: 0000000000000000
FS:  00007f763ff296c0(0000) GS:ffff8881f6e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7252417dac CR3: 00000001188b0000 CR4: 00000000003526b0
Call Trace:
 <TASK>
 set_termios+0x4ba/0x730 drivers/tty/tty_ioctl.c:492
 tty_mode_ioctl+0x492/0x7c0 drivers/tty/tty_ioctl.c:-1
 n_tty_ioctl_helper+0x97/0x530 drivers/tty/tty_ioctl.c:986
 n_tty_ioctl+0x142/0x2d0 drivers/tty/n_tty.c:2522
 tty_ioctl+0xa65/0xec0 drivers/tty/tty_io.c:2812
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0x135/0x1b0 fs/ioctl.c:893
 __x64_sys_ioctl+0x7f/0xa0 fs/ioctl.c:893
 x64_sys_call+0x1878/0x2ee0 arch/x86/include/generated/asm/syscalls_64.h:17
 do_syscall_x64 arch/x86/entry/common.c:47 [inline]
 do_syscall_64+0x57/0xf0 arch/x86/entry/common.c:78
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7f763ef9c799
Code: ff c3 66 2e 0f 1f 84 00 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
RSP: 002b:00007f763ff29028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f763f215fa0 RCX: 00007f763ef9c799
RDX: 0000200000000040 RSI: 0000000000005408 RDI: 0000000000000005
RBP: 00007f763f032bd9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f763f216038 R14: 00007f763f215fa0 R15: 00007ffd3b194d18
 </TASK>