=====================================
WARNING: bad unlock balance detected!
4.15.0-rc7+ #261 Not tainted
-------------------------------------
syz-executor4/28775 is trying to release lock (mrt_lock) at:
[<000000007e415d1c>] 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-executor4/28775:
 #0:  (sb_writers#7){.+.+}, at: [<00000000f6552a39>] file_start_write include/linux/fs.h:2715 [inline]
 #0:  (sb_writers#7){.+.+}, at: [<00000000f6552a39>] do_sendfile+0xada/0xe80 fs/read_write.c:1412
 #1:  (&p->lock){+.+.}, at: [<00000000185ef94f>] seq_read+0xd5/0x13d0 fs/seq_file.c:165

stack backtrace:
CPU: 1 PID: 28775 Comm: syz-executor4 Not tainted 4.15.0-rc7+ #261
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:3479
 __lock_release kernel/locking/lockdep.c:3685 [inline]
 lock_release+0x6fe/0xa40 kernel/locking/lockdep.c:3933
 __raw_read_unlock include/linux/rwlock_api_smp.h:225 [inline]
 _raw_read_unlock+0x1a/0x30 kernel/locking/spinlock.c:248
 ipmr_mfc_seq_stop+0xe1/0x130 net/ipv6/ip6mr.c:553
 traverse+0x3bc/0xa00 fs/seq_file.c:135
 seq_read+0x96a/0x13d0 fs/seq_file.c:189
 proc_reg_read+0xef/0x170 fs/proc/inode.c:217
 do_loop_readv_writev fs/read_write.c:673 [inline]
 do_iter_read+0x3d2/0x5a0 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+0x10a/0x160 fs/splice.c:880
 splice_direct_to_actor+0x242/0x820 fs/splice.c:952
 do_splice_direct+0x29b/0x3c0 fs/splice.c:1061
 do_sendfile+0x5c9/0xe80 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+0x23/0x9a
RIP: 0033:0x452cf9
RSP: 002b:00007f3b52172c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000452cf9
RDX: 00000000203c4ff8 RSI: 0000000000000013 RDI: 0000000000000013
RBP: 0000000000000109 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000000003ff R11: 0000000000000212 R12: 00000000006ef978
R13: 00000000ffffffff R14: 00007f3b521736d4 R15: 0000000000000000
WARNING: CPU: 1 PID: 28775 at lib/usercopy.c:26 _copy_to_user+0xb5/0xc0 lib/usercopy.c:26