netdev - Re: [PATCH v2 net-next] net: hsr: fix suspicious usage in hsr_node_get

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Message-ID: <141d43cc-6b66-2fcf-4703-70db51859960@gmail.com>
Date:   Thu, 10 Feb 2022 10:17:40 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Juhee Kang <claudiajkang@...il.com>, davem@...emloft.net,
        kuba@...nel.org, netdev@...r.kernel.org
Cc:     ennoerlangen@...il.com, george.mccollister@...il.com,
        olteanv@...il.com, marco.wenzel@...berle.de,
        syzbot+f0eb4f3876de066b128c@...kaller.appspotmail.com
Subject: Re: [PATCH v2 net-next] net: hsr: fix suspicious usage in
 hsr_node_get_first()


On 2/10/22 09:47, Eric Dumazet wrote:
>
> On 2/10/22 08:23, Juhee Kang wrote:
>> Currently, to dereference hlist_node which is result of 
>> hlist_first_rcu(),
>> rcu_dereference() is used. But, suspicious RCU warnings occur because
>> the caller doesn't acquire RCU. So it was solved by adding 
>> rcu_read_lock().
>>
>> The kernel test robot reports:
>>      [   53.750001][ T3597] =============================
>>      [   53.754849][ T3597] WARNING: suspicious RCU usage
>>      [   53.759833][ T3597] 5.17.0-rc2-syzkaller-00903-g45230829827b 
>> #0 Not tainted
>>      [   53.766947][ T3597] -----------------------------
>>      [   53.771840][ T3597] net/hsr/hsr_framereg.c:34 suspicious 
>> rcu_dereference_check() usage!
>>      [   53.780129][ T3597] other info that might help us debug this:
>>      [   53.790594][ T3597] rcu_scheduler_active = 2, debug_locks = 1
>>      [   53.798896][ T3597] 2 locks held by syz-executor.0/3597:
>
>
> Please include whole stack.
>
>
>>
>> Fixes: 4acc45db7115 ("net: hsr: use hlist_head instead of list_head 
>> for mac addresses")
>> Reported-by: Eric Dumazet <eric.dumazet@...il.com>
>> Reported-by: syzbot+f0eb4f3876de066b128c@...kaller.appspotmail.com
>> Signed-off-by: Juhee Kang <claudiajkang@...il.com>
>> ---
>> v2:
>>   - rebase current net-next tree
>>
>>   net/hsr/hsr_framereg.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/net/hsr/hsr_framereg.c b/net/hsr/hsr_framereg.c
>> index b3c6ffa1894d..92abdf855327 100644
>> --- a/net/hsr/hsr_framereg.c
>> +++ b/net/hsr/hsr_framereg.c
>> @@ -31,7 +31,10 @@ struct hsr_node *hsr_node_get_first(struct 
>> hlist_head *head)
>>   {
>>       struct hlist_node *first;
>>   +    rcu_read_lock();
>>       first = rcu_dereference(hlist_first_rcu(head));
>> +    rcu_read_unlock();
>> +
>>       if (first)
>>           return hlist_entry(first, struct hsr_node, mac_list);
>
>
> This is not fixing anything, just silence the warning.



I suggest replacing rcu_dereference() by rcu_dereference_rtnl()