=====================================
WARNING: bad unlock balance detected!
4.15.0-rc2+ #209 Not tainted
-------------------------------------
syz-executor3/27954 is trying to release lock (mrt_lock) at:
[<00000000a83c0bac>] ipmr_mfc_seq_stop+0xe1/0x130 net/ipv6/ip6mr.c:553
but there are no more locks to release!

other info that might help us debug this:
2 locks held by syz-executor3/27954:
 #0:  (sb_writers#6){.+.+}, at: [<00000000193fd4e4>] file_start_write include/linux/fs.h:2715 [inline]
 #0:  (sb_writers#6){.+.+}, at: [<00000000193fd4e4>] do_sendfile+0xaec/0xe90 fs/read_write.c:1412
 #1:  (&p->lock){+.+.}, at: [<000000001fc1cfb6>] seq_read+0xd5/0x13d0 fs/seq_file.c:165

stack backtrace:
CPU: 0 PID: 27954 Comm: syz-executor3 Not tainted 4.15.0-rc2+ #209
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 print_unlock_imbalance_bug+0x12f/0x140 kernel/locking/lockdep.c:3561
 __lock_release kernel/locking/lockdep.c:3775 [inline]
 lock_release+0x5f9/0xda0 kernel/locking/lockdep.c:4023
 __raw_read_unlock include/linux/rwlock_api_smp.h:225 [inline]
 _raw_read_unlock+0x1a/0x30 kernel/locking/spinlock.c:255
 ipmr_mfc_seq_stop+0xe1/0x130 net/ipv6/ip6mr.c:553
 seq_read+0xc42/0x13d0 fs/seq_file.c:277
 proc_reg_read+0xef/0x170 fs/proc/inode.c:217
 do_loop_readv_writev fs/read_write.c:673 [inline]
 do_iter_read+0x3db/0x5b0 fs/read_write.c:897
 vfs_readv+0x121/0x1c0 fs/read_write.c:959
 kernel_readv fs/splice.c:361 [inline]
 default_file_splice_read+0x508/0xae0 fs/splice.c:416
 do_splice_to+0x110/0x170 fs/splice.c:880
 splice_direct_to_actor+0x242/0x820 fs/splice.c:952
 do_splice_direct+0x2a7/0x3d0 fs/splice.c:1061
 do_sendfile+0x5d5/0xe90 fs/read_write.c:1413
 SYSC_sendfile64 fs/read_write.c:1468 [inline]
 SyS_sendfile64+0xbd/0x160 fs/read_write.c:1460
 entry_SYSCALL_64_fastpath+0x1f/0x96
RIP: 0033:0x4529d9
RSP: 002b:00007fc90155ac58 EFLAGS: 00000212 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007fc90155b700 RCX: 00000000004529d9
RDX: 0000000020693000 RSI: 0000000000000013 RDI: 0000000000000013
RBP: 0000000000a6f880 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000009 R11: 0000000000000212 R12: 0000000000000000
R13: 0000000000a6f7ff R14: 00007fc90155b9c0 R15: 0000000000000002
WARNING: CPU: 0 PID: 27954 at lib/usercopy.c:26 _copy_to_user+0xb5/0xc0 lib/usercopy.c:26