Warning: Permanently added '10.128.0.252' (ECDSA) to the list of known hosts.
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syzkaller login: [   36.088215] refcount_t: underflow; use-after-free.
[   36.094828] ------------[ cut here ]------------
[   36.099754] WARNING: CPU: 1 PID: 8196 at lib/refcount.c:281 refcount_dec_not_one.cold+0x18/0x25
[   36.108728] Kernel panic - not syncing: panic_on_warn set ...
[   36.108728] 
[   36.116139] CPU: 1 PID: 8196 Comm: systemd-udevd Not tainted 4.14.229-syzkaller #0
[   36.124048] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
[   36.133520] Call Trace:
[   36.136178]  dump_stack+0x1b2/0x281
[   36.139833]  panic+0x1f9/0x42d
[   36.143130]  ? add_taint.cold+0x16/0x16
[   36.147141]  ? refcount_dec_not_one.cold+0x18/0x25
[   36.152112]  ? refcount_dec_not_one.cold+0x18/0x25
[   36.157102]  __warn.cold+0x20/0x44
[   36.160708]  ? ist_end_non_atomic+0x10/0x10
[   36.165281]  ? refcount_dec_not_one.cold+0x18/0x25
[   36.170281]  report_bug+0x208/0x250
[   36.173995]  do_error_trap+0x195/0x2d0
[   36.177953]  ? math_error+0x2d0/0x2d0
[   36.181958]  ? ___preempt_schedule+0x16/0x18
[   36.186571]  ? trace_hardirqs_off_thunk+0x1a/0x1c
[   36.192394]  invalid_op+0x1b/0x40
[   36.195882] RIP: 0010:refcount_dec_not_one.cold+0x18/0x25
[   36.201415] RSP: 0018:ffff888095fffc38 EFLAGS: 00010286
[   36.206807] RAX: 0000000000000026 RBX: 0000000000000000 RCX: 0000000000000000
[   36.214176] RDX: 0000000000000000 RSI: ffffffff878bbbc0 RDI: ffffed1012bfff7d
[   36.221465] RBP: ffff8880abd170d8 R08: 0000000000000026 R09: 0000000000000000
[   36.228751] R10: 0000000000000000 R11: 0000000000000000 R12: 00000000ffffffff
[   36.236014] R13: 0000000000000000 R14: ffffed101150df46 R15: ffff8880abd170e8
[   36.243417]  ? refcount_dec_not_one.cold+0x18/0x25
[   36.248383]  ? trace_hardirqs_on_caller+0x3a8/0x580
[   36.253460]  refcount_dec_and_mutex_lock+0x1a/0x60
[   36.258423]  nbd_config_put+0x506/0x810
[   36.262448]  nbd_release+0xdf/0x150
[   36.266104]  ? nbd_queue_rq+0xc50/0xc50
[   36.270124]  __blkdev_put+0x5aa/0x800
[   36.273961]  ? revalidate_disk+0x1f0/0x1f0
[   36.278223]  ? locks_remove_file+0x2cd/0x420
[   36.282689]  ? blkdev_put+0x75/0x4c0
[   36.286429]  ? blkdev_put+0x4c0/0x4c0
[   36.290285]  blkdev_close+0x86/0xb0
[   36.294090]  __fput+0x25f/0x7a0
[   36.297417]  task_work_run+0x11f/0x190
[   36.301321]  exit_to_usermode_loop+0x1ad/0x200
[   36.305942]  do_syscall_64+0x4a3/0x640
[   36.309920]  entry_SYSCALL_64_after_hwframe+0x46/0xbb
[   36.315119] RIP: 0033:0x7fcb8b2b8270
[   36.318867] RSP: 002b:00007ffe63bce3f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
[   36.326612] RAX: 0000000000000000 RBX: 0000000000000007 RCX: 00007fcb8b2b8270
[   36.333885] RDX: 00007fcb8b2a2b58 RSI: 0000000000000000 RDI: 0000000000000007
[   36.341169] RBP: 00007fcb8c172710 R08: 1f46ba4b2ced49c4 R09: 0000000000000013
[   36.348495] R10: 0000000000000116 R11: 0000000000000246 R12: 0000000000000002
[   36.355963] R13: 0000000000000000 R14: 0000563277b84d20 R15: 0000000000000007
[   36.364187] Kernel Offset: disabled
[   36.367914] Rebooting in 86400 seconds..