[....] Starting enhanced syslogd: rsyslogd[?25l[?1c7[ ok 8[?25h[?0c. [ 41.482467][ T26] audit: type=1800 audit(1555820237.749:25): pid=7768 uid=0 auid=4294967295 ses=4294967295 subj==unconfined op=collect_data cause=failed(directio) comm="startpar" name="cron" dev="sda1" ino=2414 res=0 [ 41.523025][ T26] audit: type=1800 audit(1555820237.759:26): pid=7768 uid=0 auid=4294967295 ses=4294967295 subj==unconfined op=collect_data cause=failed(directio) comm="startpar" name="mcstrans" dev="sda1" ino=2457 res=0 [ 41.562323][ T26] audit: type=1800 audit(1555820237.759:27): pid=7768 uid=0 auid=4294967295 ses=4294967295 subj==unconfined op=collect_data cause=failed(directio) comm="startpar" name="restorecond" dev="sda1" ino=2436 res=0 [....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c. [....] Starting OpenBSD Secure Shell server: sshd[?25l[?1c7[ ok 8[?25h[?0c. Debian GNU/Linux 7 syzkaller ttyS0 Warning: Permanently added '10.128.1.53' (ECDSA) to the list of known hosts. executing program syzkaller login: [ 52.195634][ T7920] ------------[ cut here ]------------ [ 52.201409][ T7920] percpu_ref_kill_and_confirm called more than once on io_ring_ctx_ref_free! [ 52.201801][ T7920] WARNING: CPU: 0 PID: 7920 at lib/percpu-refcount.c:335 percpu_ref_kill_and_confirm+0x341/0x3b0 [ 52.221335][ T7920] Kernel panic - not syncing: panic_on_warn set ... [ 52.227963][ T7920] CPU: 0 PID: 7920 Comm: syz-executor875 Not tainted 5.1.0-rc5+ #78 [ 52.235941][ T7920] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 52.246031][ T7920] Call Trace: [ 52.249359][ T7920] dump_stack+0x172/0x1f0 [ 52.253786][ T7920] ? percpu_ref_kill_and_confirm+0x340/0x3b0 [ 52.259833][ T7920] panic+0x2cb/0x65c [ 52.263854][ T7920] ? __warn_printk+0xf3/0xf3 [ 52.268465][ T7920] ? percpu_ref_kill_and_confirm+0x341/0x3b0 [ 52.274467][ T7920] ? __sanitizer_cov_trace_const_cmp4+0x16/0x20 [ 52.280752][ T7920] ? __warn.cold+0x5/0x45 [ 52.285106][ T7920] ? __warn+0xe8/0x1d0 [ 52.289196][ T7920] ? percpu_ref_kill_and_confirm+0x341/0x3b0 [ 52.295189][ T7920] __warn.cold+0x20/0x45 [ 52.299464][ T7920] ? vprintk_emit+0x1ce/0x6d0 [ 52.304160][ T7920] ? percpu_ref_kill_and_confirm+0x341/0x3b0 [ 52.310157][ T7920] report_bug+0x263/0x2b0 [ 52.314542][ T7920] do_error_trap+0x11b/0x200 [ 52.319158][ T7920] do_invalid_op+0x37/0x50 [ 52.323588][ T7920] ? percpu_ref_kill_and_confirm+0x341/0x3b0 [ 52.329594][ T7920] invalid_op+0x14/0x20 [ 52.333783][ T7920] RIP: 0010:percpu_ref_kill_and_confirm+0x341/0x3b0 [ 52.340397][ T7920] Code: 42 e0 2a 06 01 48 89 fa 48 c1 ea 03 80 3c 02 00 75 76 49 8b 54 24 10 48 c7 c6 a0 71 a1 87 48 c7 c7 40 71 a1 87 e8 ad 92 13 fe <0f> 0b 48 b8 00 00 00 00 00 fc ff df 4c 89 ea 48 c1 ea 03 80 3c 02 [ 52.360015][ T7920] RSP: 0018:ffff88809a9cfcf0 EFLAGS: 00010082 [ 52.366093][ T7920] RAX: 0000000000000000 RBX: 0000607f5142e3c3 RCX: 0000000000000000 [ 52.374090][ T7920] RDX: 0000000000000000 RSI: ffffffff815afcf6 RDI: ffffed1013539f90 [ 52.382091][ T7920] RBP: ffff88809a9cfd20 R08: ffff88808fbe2480 R09: fffffbfff1133639 [ 52.390069][ T7920] R10: fffffbfff1133638 R11: ffffffff8899b1c3 R12: ffff88808f96cd40 [ 52.399975][ T7920] R13: ffff88808f96cd48 R14: 0000000000000286 R15: 0000000000000000 [ 52.407980][ T7920] ? vprintk_func+0x86/0x189 [ 52.412595][ T7920] __io_uring_register+0xa7/0x1fe0 [ 52.417745][ T7920] ? __mutex_lock+0x3cd/0x1310 [ 52.422545][ T7920] ? __x64_sys_io_uring_register+0x182/0x1f0 [ 52.428549][ T7920] ? mutex_trylock+0x1e0/0x1e0 [ 52.433328][ T7920] ? io_sq_wq_submit_work+0x10f0/0x10f0 [ 52.438903][ T7920] ? kasan_check_write+0x14/0x20 [ 52.443898][ T7920] __x64_sys_io_uring_register+0x193/0x1f0 [ 52.449732][ T7920] do_syscall_64+0x103/0x610 [ 52.454334][ T7920] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 52.460225][ T7920] RIP: 0033:0x445989 [ 52.464116][ T7920] Code: e8 ec bc 02 00 48 83 c4 18 c3 0f 1f 80 00 00 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 0f 83 cb 11 fc ff c3 66 2e 0f 1f 84 00 00 00 00 [ 52.483743][ T7920] RSP: 002b:00007f2111a6bdb8 EFLAGS: 00000246 ORIG_RAX: 00000000000001ab [ 52.492175][ T7920] RAX: ffffffffffffffda RBX: 00000000006dbc38 RCX: 0000000000445989 [ 52.500333][ T7920] RDX: 0000000000000000 RSI: 0000000000000003 RDI: 0000000000000003 [ 52.508331][ T7920] RBP: 00000000006dbc30 R08: 00007f2111a6c700 R09: 0000000000000000 [ 52.516311][ T7920] R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc3c [ 52.524336][ T7920] R13: 00007fff7172171f R14: 00007f2111a6c9c0 R15: 0000000000000002 [ 52.533532][ T7920] Kernel Offset: disabled [ 52.537975][ T7920] Rebooting in 86400 seconds..