------------[ cut here ]------------
DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) && !rwsem_test_oflags(sem, RWSEM_NONSPINNABLE)): count = 0x0, magic = 0xffff8880430bd058, owner = 0x0, curr 0xffff8880006bc900, list empty
WARNING: CPU: 0 PID: 5327 at kernel/locking/rwsem.c:1381 __up_write kernel/locking/rwsem.c:1380 [inline]
WARNING: CPU: 0 PID: 5327 at kernel/locking/rwsem.c:1381 up_write+0x3a2/0x420 kernel/locking/rwsem.c:1643
Modules linked in:
CPU: 0 UID: 0 PID: 5327 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:__up_write kernel/locking/rwsem.c:1380 [inline]
RIP: 0010:up_write+0x3a2/0x420 kernel/locking/rwsem.c:1643
Code: d0 48 c7 c7 20 ff 6a 8b 48 c7 c6 40 01 6b 8b 48 8b 14 24 4c 89 f1 4d 89 e0 4c 8b 4c 24 08 41 52 e8 c3 35 e6 ff 48 83 c4 08 90 <0f> 0b 90 90 e9 6d fd ff ff 48 c7 c1 94 3e 7d 8f 80 e1 07 80 c1 03
RSP: 0018:ffffc9000d497c68 EFLAGS: 00010282
RAX: 06bd97033099d500 RBX: ffff8880430bd058 RCX: ffff8880006bc900
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000002
RBP: dffffc0000000000 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff1bba684 R12: 0000000000000000
R13: ffff8880430bd0b0 R14: ffff8880430bd058 R15: 1ffff11008617a0c
FS:  00007f33881f56c0(0000) GS:ffff88808d730000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffc43aa6dc0 CR3: 00000000117e8000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 inode_unlock include/linux/fs.h:990 [inline]
 __unlock_mount fs/namespace.c:2780 [inline]
 unlock_mount+0xbd/0x3a0 fs/namespace.c:2790
 do_loopback+0x397/0x410 fs/namespace.c:2999
 do_mount fs/namespace.c:4041 [inline]
 __do_sys_mount fs/namespace.c:4229 [inline]
 __se_sys_mount+0x313/0x410 fs/namespace.c:4206
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f338bd8f749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f33881f5038 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f338bfe6180 RCX: 00007f338bd8f749
RDX: 0000000000000000 RSI: 00002000000001c0 RDI: 0000200000000080
RBP: 00007f338be13f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000002101c84 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f338bfe6218 R14: 00007f338bfe6180 R15: 00007ffc43aa75a8
 </TASK>