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

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Date:	Thu, 31 Mar 2016 18:45:24 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
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 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()

Thanks !