syzbot

=====================================
[ BUG: bad unlock balance detected! ]
4.4.114-g4e74e98 #5 Not tainted
-------------------------------------
syz-executor7/9485 is trying to release lock (mrt_lock) at:
[<ffffffff833c7904>] ipmr_mfc_seq_stop+0xe4/0x140 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-executor7/9485:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff8157ac1f>] __fdget_pos+0x9f/0xc0 fs/file.c:780
 #1:  (&p->lock){+.+.+.}, at: [<ffffffff8158d6cd>] seq_read+0xdd/0x1270 fs/seq_file.c:178

stack backtrace:
CPU: 1 PID: 9485 Comm: syz-executor7 Not tainted 4.4.114-g4e74e98 #5
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 f1073ee38eeb3f05 ffff8800aa57f920 ffffffff81d03d2d
 ffffffff84771c98 ffff8801d96f4800 ffffffff833c7904 ffffffff84771c98
 ffff8801d96f50a8 ffff8800aa57f950 ffffffff81233354 dffffc0000000000
Call Trace:
 [<ffffffff81d03d2d>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d03d2d>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff81233354>] print_unlock_imbalance_bug+0x174/0x1a0 kernel/locking/lockdep.c:3266
 [<ffffffff8123e1ea>] __lock_release kernel/locking/lockdep.c:3408 [inline]
 [<ffffffff8123e1ea>] lock_release+0x72a/0xc10 kernel/locking/lockdep.c:3611
 [<ffffffff83773bda>] __raw_read_unlock include/linux/rwlock_api_smp.h:225 [inline]
 [<ffffffff83773bda>] _raw_read_unlock+0x1a/0x50 kernel/locking/spinlock.c:255
 [<ffffffff833c7904>] ipmr_mfc_seq_stop+0xe4/0x140 net/ipv6/ip6mr.c:553
 [<ffffffff8158e070>] seq_read+0xa80/0x1270 fs/seq_file.c:283
 [<ffffffff81665d1f>] proc_reg_read+0xef/0x170 fs/proc/inode.c:202
 [<ffffffff8151d891>] do_loop_readv_writev+0x141/0x1e0 fs/read_write.c:680
 [<ffffffff8151fbed>] do_readv_writev+0x5dd/0x6e0 fs/read_write.c:810
 [<ffffffff8151fd68>] vfs_readv+0x78/0xb0 fs/read_write.c:834
 [<ffffffff81522099>] SYSC_readv fs/read_write.c:860 [inline]
 [<ffffffff81522099>] SyS_readv+0xd9/0x240 fs/read_write.c:852
 [<ffffffff837742df>] entry_SYSCALL_64_fastpath+0x1c/0x98