netdev - Re: [PATCH net 4/4] tcp: various missing rcu_read_lock around __sk_dst

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Message-ID: <56FDD67E.2040904@stressinduktion.org>
Date:	Fri, 1 Apr 2016 04:01:34 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	sasha.levin@...cle.com, daniel@...earbox.net,
	alexei.starovoitov@...il.com, mkubecek@...e.cz
Subject: Re: [PATCH net 4/4] tcp: various missing rcu_read_lock around
 __sk_dst_get

On 01.04.2016 03:45, Eric Dumazet wrote:
> On Thu, 2016-03-31 at 18:39 -0700, Eric Dumazet wrote:
>> On Fri, 2016-04-01 at 03:36 +0200, Hannes Frederic Sowa wrote:
>>> On Fri, Apr 1, 2016, at 03:19, Eric Dumazet wrote:
>>>> Thanks.
>>>>
>>>> As you can see, release_sock() messes badly lockdep (once your other
>>>> patches are in )
>>>>
>>>> Once we properly fix release_sock() and/or __release_sock(), all these
>>>> false positives disappear.
>>>
>>> This was a loopback connection. I need to study release_sock and
>>> __release_sock more as I cannot currently see an issue with the lockdep
>>> handling.
>>
>> Okay, please try :
>>
>> diff --git a/net/core/sock.c b/net/core/sock.c
>> index b67b9aedb230..570dcd91d64e 100644
>> --- a/net/core/sock.c
>> +++ b/net/core/sock.c
>> @@ -2429,10 +2429,6 @@ EXPORT_SYMBOL(lock_sock_nested);
>>
>>   void release_sock(struct sock *sk)
>>   {
>> -	/*
>> -	 * The sk_lock has mutex_unlock() semantics:
>> -	 */
>> -	mutex_release(&sk->sk_lock.dep_map, 1, _RET_IP_);
>>
>>   	spin_lock_bh(&sk->sk_lock.slock);
>>   	if (sk->sk_backlog.tail)
>> @@ -2445,6 +2441,10 @@ void release_sock(struct sock *sk)
>>   		sk->sk_prot->release_cb(sk);
>>
>>   	sock_release_ownership(sk);
>> +	/*
>> +	 * The sk_lock has mutex_unlock() semantics:
>> +	 */
>> +	mutex_release(&sk->sk_lock.dep_map, 1, _RET_IP_);
>>   	if (waitqueue_active(&sk->sk_lock.wq))
>>   		wake_up(&sk->sk_lock.wq);
>>   	spin_unlock_bh(&sk->sk_lock.slock);
>
> Also take a look at commit c3f9b01849ef3bc69024990092b9f42e20df7797
>
> We might need to include the mutex_release() in sock_release_ownership()

I thought so first, as well. But given the double check for the 
spin_lock and the "mutex" we end up with the same result for the 
lockdep_sock_is_held check.

Do you see other consequences?

Thanks,
Hannes