=====================================
WARNING: bad unlock balance detected!
4.15.0-rc9+ #192 Not tainted
-------------------------------------
syz-executor2/23929 is trying to release lock (mrt_lock) at:
[<00000000899d2d8d>] 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-executor2/23929:
 #0:  (sb_writers#7){.+.+}, at: [<000000007f0a2a6b>] file_start_write include/linux/fs.h:2715 [inline]
 #0:  (sb_writers#7){.+.+}, at: [<000000007f0a2a6b>] do_sendfile+0xada/0xe80 fs/read_write.c:1412
 #1:  (&p->lock){+.+.}, at: [<00000000724cf729>] seq_read+0xd5/0x13d0 fs/seq_file.c:165

stack backtrace:
CPU: 1 PID: 23929 Comm: syz-executor2 Not tainted 4.15.0-rc9+ #192
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
 C_SYSC_sendfile fs/read_write.c:1489 [inline]
 compat_SyS_sendfile+0xea/0x1a0 fs/read_write.c:1478
 do_syscall_32_irqs_on arch/x86/entry/common.c:327 [inline]
 do_fast_syscall_32+0x3ee/0xf9d arch/x86/entry/common.c:389
 entry_SYSENTER_compat+0x54/0x63 arch/x86/entry/entry_64_compat.S:129
RIP: 0023:0xf7f2ec79
RSP: 002b:00000000f770908c EFLAGS: 00000296 ORIG_RAX: 00000000000000bb
RAX: ffffffffffffffda RBX: 0000000000000013 RCX: 0000000000000013
RDX: 00000000205b3000 RSI: 000000000000008b RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
WARNING: CPU: 1 PID: 23929 at lib/usercopy.c:26 _copy_to_user+0xb5/0xc0 lib/usercopy.c:26