=====================================
[ BUG: bad unlock balance detected! ]
4.9.76-gf0f6293 #22 Not tainted
-------------------------------------
syz-executor3/6814 is trying to release lock (mrt_lock) at:
[<ffffffff834e6574>] 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-executor3/6814:
 #0:  (sb_writers#7){.+.+.+}, at: [<ffffffff8157190f>] file_start_write include/linux/fs.h:2619 [inline]
 #0:  (sb_writers#7){.+.+.+}, at: [<ffffffff8157190f>] do_sendfile+0x9ff/0xd30 fs/read_write.c:1400
 #1:  (&p->lock){+.+.+.}, at: [<ffffffff815e75ad>] seq_read+0xdd/0x1290 fs/seq_file.c:178

stack backtrace:
CPU: 0 PID: 6814 Comm: syz-executor3 Not tainted 4.9.76-gf0f6293 #22
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801c58ef238 ffffffff81d93149 ffffffff849b67b8 ffff8801cdf3b000
 ffffffff834e6574 ffffffff849b67b8 ffff8801cdf3b888 ffff8801c58ef268
 ffffffff81236cd4 dffffc0000000000 ffffffff849b67b8 00000000ffffffff
Call Trace:
 [<ffffffff81d93149>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d93149>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81236cd4>] print_unlock_imbalance_bug+0x174/0x1a0 kernel/locking/lockdep.c:3398
 [<ffffffff8123f7a8>] __lock_release kernel/locking/lockdep.c:3540 [inline]
 [<ffffffff8123f7a8>] lock_release+0x6f8/0xb80 kernel/locking/lockdep.c:3775
 [<ffffffff838b05fa>] __raw_read_unlock include/linux/rwlock_api_smp.h:225 [inline]
 [<ffffffff838b05fa>] _raw_read_unlock+0x1a/0x50 kernel/locking/spinlock.c:255
 [<ffffffff834e6574>] ipmr_mfc_seq_stop+0xe4/0x140 net/ipv6/ip6mr.c:553
 [<ffffffff815e7f53>] seq_read+0xa83/0x1290 fs/seq_file.c:283
 [<ffffffff816c0c4f>] proc_reg_read+0xef/0x170 fs/proc/inode.c:202
 [<ffffffff8156b571>] do_loop_readv_writev.part.17+0x141/0x1e0 fs/read_write.c:714
 [<ffffffff8156f3e0>] do_loop_readv_writev fs/read_write.c:880 [inline]
 [<ffffffff8156f3e0>] do_readv_writev+0x520/0x750 fs/read_write.c:874
 [<ffffffff8156f694>] vfs_readv+0x84/0xc0 fs/read_write.c:898
 [<ffffffff8160e74f>] kernel_readv fs/splice.c:363 [inline]
 [<ffffffff8160e74f>] default_file_splice_read+0x43f/0x7a0 fs/splice.c:435
 [<ffffffff8160d84a>] do_splice_to+0x10a/0x160 fs/splice.c:899
 [<ffffffff8160daed>] splice_direct_to_actor+0x24d/0x800 fs/splice.c:971
 [<ffffffff8160e247>] do_splice_direct+0x1a7/0x270 fs/splice.c:1080
 [<ffffffff8157145b>] do_sendfile+0x54b/0xd30 fs/read_write.c:1401
 [<ffffffff81573511>] C_SYSC_sendfile fs/read_write.c:1477 [inline]
 [<ffffffff81573511>] compat_SyS_sendfile+0xd1/0x160 fs/read_write.c:1466
 [<ffffffff81006fc7>] do_syscall_32_irqs_on arch/x86/entry/common.c:322 [inline]
 [<ffffffff81006fc7>] do_fast_syscall_32+0x2f7/0x890 arch/x86/entry/common.c:384
 [<ffffffff838b2334>] entry_SYSENTER_compat+0x74/0x83 arch/x86/entry/entry_64_compat.S:127