------------[ cut here ]------------
WARNING: CPU: 0 PID: 9608 at fs/namespace.c:1186 mntput_no_expire+0xada/0xcd0 fs/namespace.c:1186
Modules linked in:
CPU: 0 PID: 9608 Comm: kworker/0:5 Not tainted 5.12.0-rc6-next-20210409-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events free_ipc
RIP: 0010:mntput_no_expire+0xada/0xcd0 fs/namespace.c:1186
Code: 30 84 c0 0f 84 b9 fe ff ff 3c 03 0f 8f b1 fe ff ff 4c 89 44 24 10 e8 15 42 ec ff 4c 8b 44 24 10 e9 9d fe ff ff e8 16 77 a7 ff <0f> 0b e9 19 fd ff ff e8 0a 77 a7 ff e8 45 cc 42 07 31 ff 89 c5 89
RSP: 0018:ffffc9000c347c08 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 1ffff92001868f87 RCX: 0000000000000000
RDX: ffff88802c8f3900 RSI: ffffffff81ccb91a RDI: 0000000000000003
RBP: ffff8880261a5e00 R08: 0000000000000000 R09: ffffffff8fafc8af
R10: ffffffff81ccb631 R11: 0000000000000000 R12: 0000000000000008
R13: ffffc9000c347c58 R14: 00000000ffffffff R15: 0000000000000002
FS:  0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f476b8d1280 CR3: 0000000073cf3000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 mntput fs/namespace.c:1232 [inline]
 kern_unmount fs/namespace.c:4277 [inline]
 kern_unmount+0xb5/0xe0 fs/namespace.c:4271
 free_ipc_ns ipc/namespace.c:123 [inline]
 free_ipc+0xf0/0x200 ipc/namespace.c:141
 process_one_work+0x98d/0x1600 kernel/workqueue.c:2275
 worker_thread+0x64c/0x1120 kernel/workqueue.c:2421
 kthread+0x3b1/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294