netdev - Re: BUG in net/l2tp/l2tp

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Date:	Wed, 09 Oct 2013 04:05:30 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	François Cachereul <f.cachereul@...halink.fr>
Cc:	James Chapman <jchapman@...alix.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: BUG in net/l2tp/l2tp_core.c

On Wed, 2013-10-09 at 12:11 +0200, François Cachereul wrote:
> Hi,
> 
> I got the following BUG when using l2tp modules with smp kernel.
> I noticed that l2tp_xmit_skb uses bh_lock_sock/bh_unlok_sock which
> doesn't seem to be correct because it does a lot of stuff and probably
> sleep before releasing the lock. I try replacing
> bh_lock_sock/bh_unlock_sock with lock_sock/release_sock and the BUG
> doesn't happened anymore. Is it correct ?
> 
> Regards
> François
> 

At first glance, you might read commit
6af88da14ee284aaad6e4326da09a89191ab6165
("l2tp: Fix locking in l2tp_core.c")

l2tp_eth_dev_xmit() is called from BH context, so you cannot use
lock_sock()

Try the following patch instead :

diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
index f0a7ada..ffda81e 100644
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -353,7 +353,9 @@ static int pppol2tp_sendmsg(struct kiocb *iocb, struct socket *sock, struct msgh
 		goto error_put_sess_tun;
 	}
 
+	local_bh_disable();
 	l2tp_xmit_skb(session, skb, session->hdr_len);
+	local_bh_enable();
 
 	sock_put(ps->tunnel_sock);
 	sock_put(sk);
@@ -422,7 +424,9 @@ static int pppol2tp_xmit(struct ppp_channel *chan, struct sk_buff *skb)
 	skb->data[0] = ppph[0];
 	skb->data[1] = ppph[1];
 
+	local_bh_disable();
 	l2tp_xmit_skb(session, skb, session->hdr_len);
+	local_bh_enable();
 
 	sock_put(sk_tun);
 	sock_put(sk);


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