INFO: task syz.2.51:6134 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.2.51        state:D stack:26008 pid:6134  tgid:6089  ppid:5606   task_flags:0x400140 flags:0x00080002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5504 [inline]
 __schedule+0x1709/0x5530 kernel/sched/core.c:7228
 __schedule_loop kernel/sched/core.c:7307 [inline]
 rt_mutex_schedule+0x76/0xf0 kernel/sched/core.c:7603
 rt_mutex_slowlock_block kernel/locking/rtmutex.c:1670 [inline]
 __rt_mutex_slowlock kernel/locking/rtmutex.c:1747 [inline]
 __rt_mutex_slowlock_locked+0x1f84/0x25b0 kernel/locking/rtmutex.c:1787
 __rwbase_read_lock+0xc3/0x180 kernel/locking/rwbase_rt.c:114
 rwbase_read_lock kernel/locking/rwbase_rt.c:147 [inline]
 __down_read kernel/locking/rwsem.c:1502 [inline]
 down_read+0x132/0x200 kernel/locking/rwsem.c:1576
 btrfs_mksubvol+0x261/0x10c0 fs/btrfs/ioctl.c:881
 __btrfs_ioctl_snap_create+0x24a/0x6b0 fs/btrfs/ioctl.c:1160
 btrfs_ioctl_snap_create+0x134/0x190 fs/btrfs/ioctl.c:1217
 btrfs_ioctl+0x649/0xd60 fs/btrfs/ioctl.c:-1
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xff/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3b3e8bce59
RSP: 002b:00007f3b3cad4028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f3b3eb36180 RCX: 00007f3b3e8bce59
RDX: 0000200000003480 RSI: 000000005000940e RDI: 0000000000000006
RBP: 00007f3b3e952d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f3b3eb36218 R14: 00007f3b3eb36180 R15: 00007ffeb76c1a68
 </TASK>
INFO: lockdep is turned off.
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 39 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
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 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 17 Comm: pr/legacy Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:preempt_count_add+0x115/0x190 kernel/sched/core.c:5971
Code: 04 38 84 c0 75 78 83 3d dc fe f8 0d 00 75 13 48 8d 3d 5f 0b fc 0d 48 c7 c6 a0 1a 4c 8b 67 48 0f b9 3a 90 89 df e9 5f ff ff ff <48> c7 c1 80 15 80 99 80 e1 07 80 c1 03 38 c1 0f 8c 01 ff ff ff 89
RSP: 0000:ffffc90000167a08 EFLAGS: 00000202
RAX: 0000000000000004 RBX: 0000000000000899 RCX: 0000000000000000
RDX: 0000000000000082 RSI: ffffffff8baa3a60 RDI: 0000000000000001
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: ffffffff8b2eec40 R12: 1ffffffff33771de
R13: 00000000ffffffff R14: 0000008214e967c0 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff888125fd3000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007faa655d0050 CR3: 000000005d438000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 delay_tsc+0x65/0xc0 arch/x86/lib/delay.c:79
 udelay include/asm-generic/delay.h:62 [inline]
 wait_for_lsr+0x14d/0x300 drivers/tty/serial/8250/8250_port.c:1988
 serial8250_fifo_wait_for_lsr_thre drivers/tty/serial/8250/8250_port.c:3229 [inline]
 serial8250_console_fifo_write drivers/tty/serial/8250/8250_port.c:3294 [inline]
 serial8250_console_write+0x113a/0x1b40 drivers/tty/serial/8250/8250_port.c:3379
 console_emit_next_record kernel/printk/printk.c:3163 [inline]
 console_flush_one_record+0x642/0xb50 kernel/printk/printk.c:3269
 legacy_kthread_func+0x1b6/0x250 kernel/printk/printk.c:3712
 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>