From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Ahern <dsahern@gmail.com>
Subject: Re: WARNING: suspicious RCU usage in rt6_check_expired
Date: Mon, 23 Apr 2018 09:10:03 -0600
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To: Eric Dumazet <eric.dumazet@gmail.com>,
        syzbot <syzbot+2422c9e35796659d2273@syzkaller.appspotmail.com>,
        davem@davemloft.net, kuznet@ms2.inr.ac.ru,
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        syzkaller-bugs@googlegroups.com
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On 4/23/18 7:31 AM, Eric Dumazet wrote:
>> stack backtrace:
>> CPU: 1 PID: 25958 Comm: syz-executor7 Not tainted 4.16.0+ #11
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>> Call Trace:
>>  __dump_stack lib/dump_stack.c:77 [inline]
>>  dump_stack+0x1b9/0x294 lib/dump_stack.c:113
>>  lockdep_rcu_suspicious+0x14a/0x153 kernel/locking/lockdep.c:4592
>>  rt6_check_expired+0x38b/0x3e0 net/ipv6/route.c:410
>>  ip6_negative_advice+0x67/0xc0 net/ipv6/route.c:2204
>>  dst_negative_advice include/net/sock.h:1786 [inline]
>>  sock_setsockopt+0x138f/0x1fe0 net/core/sock.c:1051
>>  __sys_setsockopt+0x2df/0x390 net/socket.c:1899
>>  SYSC_setsockopt net/socket.c:1914 [inline]
>>  SyS_setsockopt+0x34/0x50 net/socket.c:1911
>>  do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
>>  entry_SYSCALL_64_after_hwframe+0x42/0xb7

...

> 
> Added in commit a68886a691804d3f6d479ebf6825480fbafb6a00
> ("net/ipv6: Make from in rt6_info rcu protected")
> 

I missed the rcu_read_lock for this path. Will send a patch.