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

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Message-ID: <1459474756.6473.248.camel@edumazet-glaptop3.roam.corp.google.com>
Date:	Thu, 31 Mar 2016 18:39:16 -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 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);