------------[ cut here ]------------
ida_free called for id=1305 which is not allocated.
WARNING: CPU: 0 PID: 6199 at lib/idr.c:592 ida_free+0x280/0x310 lib/idr.c:592
Modules linked in:
CPU: 0 UID: 0 PID: 6199 Comm: syz.4.269 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:ida_free+0x280/0x310 lib/idr.c:592
Code: 00 00 00 00 fc ff df 48 8b 5c 24 10 48 8b 7c 24 40 48 89 de e8 d1 8a 0c 00 90 48 c7 c7 20 1b db 8c 44 89 fe e8 11 f7 0f f6 90 <0f> 0b 90 90 eb 34 e8 a5 7c 4c f6 49 bd 00 00 00 00 00 fc ff df eb
RSP: 0018:ffffc9000d5df880 EFLAGS: 00010246
RAX: 87c54425569d5400 RBX: 0000000000000a06 RCX: ffff88803d8d8000
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000002
RBP: ffffc9000d5df968 R08: ffff88801fc24293 R09: 1ffff11003f84852
R10: dffffc0000000000 R11: ffffed1003f84853 R12: 1ffff92001abbf14
R13: dffffc0000000000 R14: ffff888011d58800 R15: 0000000000000519
FS:  0000000000000000(0000) GS:ffff88808d001000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b32563fff CR3: 0000000023130000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 free_mnt_ns+0x52/0xe0 fs/namespace.c:4096
 namespace_unlock+0x529/0x760 fs/namespace.c:1701
 free_nsproxy+0x3e/0x350 kernel/nsproxy.c:188
 do_exit+0x6b0/0x2300 kernel/exit.c:960
 do_group_exit+0x21c/0x2d0 kernel/exit.c:1102
 get_signal+0x1286/0x1340 kernel/signal.c:3034
 arch_do_signal_or_restart+0x9a/0x750 arch/x86/kernel/signal.c:337
 exit_to_user_mode_loop+0x75/0x110 kernel/entry/common.c:40
 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
 do_syscall_64+0x2bd/0x3b0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fcabb78eec9
Code: Unable to access opcode bytes at 0x7fcabb78ee9f.
RSP: 002b:00007fcabc557038 EFLAGS: 00000246 ORIG_RAX: 0000000000000110
RAX: fffffffffffffff4 RBX: 00007fcabb9e5fa0 RCX: 00007fcabb78eec9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 000000002a060400
RBP: 00007fcabb811f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fcabb9e6038 R14: 00007fcabb9e5fa0 R15: 00007ffface063b8
 </TASK>