------------[ cut here ]------------
ida_free called for id=1246 which is not allocated.
WARNING: CPU: 0 PID: 5344 at lib/idr.c:592 ida_free+0x280/0x310 lib/idr.c:592
Modules linked in:
CPU: 0 UID: 0 PID: 5344 Comm: syz.0.0 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 51 ea 0b 00 90 48 c7 c7 80 31 74 8c 44 89 fe e8 21 37 56 f6 90 <0f> 0b 90 90 eb 34 e8 35 d6 92 f6 49 bd 00 00 00 00 00 fc ff df eb
RSP: 0018:ffffc9000d357880 EFLAGS: 00010246
RAX: a45d638fdd78f700 RBX: 0000000000000a06 RCX: ffff888000eda480
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000002
RBP: ffffc9000d357968 R08: ffff88801fe24293 R09: 1ffff11003fc4852
R10: dffffc0000000000 R11: ffffed1003fc4853 R12: 1ffff92001a6af14
R13: dffffc0000000000 R14: ffff88801177df00 R15: 00000000000004de
FS:  0000000000000000(0000) GS:ffff88808d98a000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000001c0ab000 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:965
 do_group_exit+0x21c/0x2d0 kernel/exit.c:1107
 get_signal+0x1285/0x1340 kernel/signal.c:3034
 arch_do_signal_or_restart+0xa0/0x790 arch/x86/kernel/signal.c:337
 exit_to_user_mode_loop+0x72/0x130 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: 0033:0x7f62e938eec9
Code: Unable to access opcode bytes at 0x7f62e938ee9f.
RSP: 002b:00007f62ea1ca038 EFLAGS: 00000246 ORIG_RAX: 0000000000000110
RAX: fffffffffffffff4 RBX: 00007f62e95e6180 RCX: 00007f62e938eec9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000022020600
RBP: 00007f62e9411f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f62e95e6218 R14: 00007f62e95e6180 R15: 00007ffe8daf4668
 </TASK>