syzbot

watchdog: BUG: soft lockup - CPU#1 stuck for 153s! [syz.8.5704:14488]
CPU#1 Utilization every 22s during lockup:
	#1: 100% system,	  1% softirq,	  1% hardirq,	  0% idle
	#2: 100% system,	  0% softirq,	  1% hardirq,	  0% idle
	#3: 100% system,	  1% softirq,	  1% hardirq,	  0% idle
	#4: 100% system,	  0% softirq,	  1% hardirq,	  0% idle
	#5: 100% system,	  0% softirq,	  1% hardirq,	  0% idle
Modules linked in:
CPU: 1 UID: 0 PID: 14488 Comm: syz.8.5704 Not tainted syzkaller #0 0b5ffdee5fcd2f7749818d1ff954e9c21353764e
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
RIP: 0010:next_peer fs/pnode.c:19 [inline]
RIP: 0010:do_make_slave fs/pnode.c:100 [inline]
RIP: 0010:change_mnt_propagation+0x13c/0xb00 fs/pnode.c:128
Code: 49 81 c4 d8 00 00 00 4c 89 e0 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df 80 3c 08 00 74 08 4c 89 e7 e8 18 51 e7 ff 4d 8b 24 24 <49> 01 dc 4c 3b 65 c8 74 66 e8 86 e3 90 ff eb 99 4d 8d 7d 30 48 89
RSP: 0018:ffffc9000a51f9c0 EFLAGS: 00000246
RAX: 1ffff1102b493a13 RBX: ffffffffffffff28 RCX: dffffc0000000000
RDX: ffffc90011053000 RSI: 000000000007ffff RDI: 0000000000080000
RBP: ffffc9000a51fa10 R08: ffff888154c5882f R09: 0000000000000000
R10: ffff888154c58820 R11: ffffed102a98b106 R12: ffff888117a93958
R13: ffff88812ee54000 R14: ffff88815a49cfe0 R15: ffff88814f229340
FS:  00007f0d766a86c0(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000110c2b4224 CR3: 0000000154c3e000 CR4: 00000000003526b0
Call Trace:
 <TASK>
 umount_tree+0xdfd/0xf70 fs/namespace.c:1803
 attach_recursive_mnt+0x6df/0x21e0 fs/namespace.c:2549
 graft_tree+0x157/0x1c0 fs/namespace.c:2684
 do_loopback+0x364/0x4b0 fs/namespace.c:2816
 path_mount+0x582/0x1050 fs/namespace.c:3858
 do_mount fs/namespace.c:3877 [inline]
 __do_sys_mount fs/namespace.c:4087 [inline]
 __se_sys_mount+0x2bd/0x480 fs/namespace.c:4064
 __x64_sys_mount+0xc3/0xf0 fs/namespace.c:4064
 x64_sys_call+0x2021/0x2ee0 arch/x86/include/generated/asm/syscalls_64.h:166
 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: 0033:0x7f0d7578f6c9
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:00007f0d766a8038 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f0d759e5fa0 RCX: 00007f0d7578f6c9
RDX: 0000000000000000 RSI: 0000200000000200 RDI: 0000200000000180
RBP: 00007f0d75811f91 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000020a5819 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f0d759e6038 R14: 00007f0d759e5fa0 R15: 00007ffc44450a98
 </TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 14513 Comm: syz.4.5715 Not tainted syzkaller #0 0b5ffdee5fcd2f7749818d1ff954e9c21353764e
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
RIP: 0010:pv_native_safe_halt+0x17/0x20 arch/x86/kernel/paravirt.c:106
Code: cc cc cc b8 34 77 c4 66 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d c3 e2 39 00 f3 0f 1e fa 55 48 89 e5 fb f4 <5d> e9 d3 54 02 00 cc cc cc b8 00 00 00 00 90 90 90 90 90 90 90 90
RSP: 0018:ffffc9000a7cf710 EFLAGS: 000002d3
RAX: ffffffff81439535 RBX: 0000000000000003 RCX: ffff88810dbb3900
RDX: 0000000000000000 RSI: 0000000000000003 RDI: 0000000000000003
RBP: ffffc9000a7cf710 R08: ffffffff8720d604 R09: 1ffffffff0e41ac0
R10: dffffc0000000000 R11: fffffbfff0e41ac1 R12: dffffc0000000000
R13: 0000000000000200 R14: 0000000000000003 R15: 1ffff920014f9ee4
FS:  0000000000000000(0000) GS:ffff8881f6e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000110c27ebfa CR3: 00000000072a8000 CR4: 00000000003526b0
DR0: 0000000000000100 DR1: 0000000000200004 DR2: 0000000000080007
DR3: 0000000000000008 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 arch_safe_halt arch/x86/include/asm/paravirt.h:112 [inline]
 kvm_wait+0x1ba/0x220 arch/x86/kernel/kvm.c:1064
 pv_wait arch/x86/include/asm/paravirt.h:596 [inline]
 pv_wait_head_or_lock kernel/locking/qspinlock_paravirt.h:466 [inline]
 __pv_queued_spin_lock_slowpath+0x78d/0xcc0 kernel/locking/qspinlock.c:508
 pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:584 [inline]
 queued_spin_lock_slowpath arch/x86/include/asm/qspinlock.h:51 [inline]
 queued_spin_lock include/asm-generic/qspinlock.h:114 [inline]
 do_raw_spin_lock include/linux/spinlock.h:187 [inline]
 __raw_spin_lock include/linux/spinlock_api_smp.h:134 [inline]
 _raw_spin_lock+0x109/0x120 kernel/locking/spinlock.c:154
 spin_lock include/linux/spinlock.h:351 [inline]
 write_seqlock include/linux/seqlock.h:876 [inline]
 lock_mount_hash fs/namespace.c:215 [inline]
 mntput_no_expire+0x147/0x6c0 fs/namespace.c:1411
 mntput+0x63/0xd0 fs/namespace.c:1466
 path_put+0x5b/0x70 fs/namei.c:569
 free_fs_struct fs/fs_struct.c:90 [inline]
 exit_fs+0xe8/0x160 fs/fs_struct.c:108
 do_exit+0x98d/0x2630 kernel/exit.c:949
 do_group_exit+0x22a/0x300 kernel/exit.c:1095
 get_signal+0x139d/0x14f0 kernel/signal.c:2933
 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: 0033:0x7f9f23bc1f85
Code: Unable to access opcode bytes at 0x7f9f23bc1f5b.
RSP: 002b:00007f9f24a17f80 EFLAGS: 00000293 ORIG_RAX: 00000000000000e6
RAX: fffffffffffffdfc RBX: 00007f9f23de6090 RCX: 00007f9f23bc1f85
RDX: 00007f9f24a17fc0 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00007f9f23c11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000000
R13: 00007f9f23de6128 R14: 00007f9f23de6090 R15: 00007fffd292c918
 </TASK>