Subject: Re: [PATCH][PPPOL2TP]: Fix SMP oops in pppol2tp driver

From: Jarek Poplawski <[email-masked]>
Date: Tue, 26 Feb 2008 21:00:33 +0100

James Chapman wrote, On 02/26/2008 01:14 PM:
...
> Luckily, I'm in the lab where my two borrowed servers are today so I 
> have access to their consoles. Hopefully I'll be able to find out why 
> there are hanging. Btw, they don't hang if I disable irqs around the 
> ppp_input() call.

Maybe you've found the same, or there is some other reason yet, but
IMHO this locking break around ppp_input() is wrong. Probably there
is needed more advanced solution, but this should fix the problem if
it really exists (isn't there possible a race e.g. between receive
from socket and from network card?).

Jarek P.
---

 drivers/net/pppol2tp.c |   16 ++++++++--------
 1 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/net/pppol2tp.c b/drivers/net/pppol2tp.c
index e0b072d..7c6fcb9 100644
--- a/drivers/net/pppol2tp.c
+++ b/drivers/net/pppol2tp.c
@@ -363,18 +363,17 @@ out:
 	spin_unlock(&session->reorder_q.lock);
 }
 
-/* Dequeue a single skb.
+/* Requeue a single skb.
  */
-static void pppol2tp_recv_dequeue_skb(struct pppol2tp_session *session, struct sk_buff *skb)
+static void pppol2tp_recv_requeue_skb(struct pppol2tp_session *session, struct sk_buff *skb)
 {
 	struct pppol2tp_tunnel *tunnel = session->tunnel;
 	int length = PPPOL2TP_SKB_CB(skb)->length;
 	struct sock *session_sock = NULL;
 
-	/* We're about to requeue the skb, so unlink it and return resources
+	/* We're about to requeue the skb, so return resources
 	 * to its current owner (a socket receive buffer).
 	 */
-	skb_unlink(skb, &session->reorder_q);
 	skb_orphan(skb);
 
 	tunnel->stats.rx_packets++;
@@ -436,14 +435,14 @@ static void pppol2tp_recv_dequeue_skb(struct pppol2tp_session *session, struct s
 static void pppol2tp_recv_dequeue(struct pppol2tp_session *session)
 {
 	struct sk_buff *skb;
-	struct sk_buff *tmp;
 
 	/* If the pkt at the head of the queue has the nr that we
 	 * expect to send up next, dequeue it and any other
 	 * in-sequence packets behind it.
 	 */
+again:
 	spin_lock(&session->reorder_q.lock);
-	skb_queue_walk_safe(&session->reorder_q, skb, tmp) {
+	skb_queue_walk(&session->reorder_q, skb) {
 		if (time_after(jiffies, PPPOL2TP_SKB_CB(skb)->expires)) {
 			session->stats.rx_seq_discards++;
 			session->stats.rx_errors++;
@@ -469,9 +468,10 @@ static void pppol2tp_recv_dequeue(struct pppol2tp_session *session)
 				goto out;
 			}
 		}
+		__skb_unlink(skb, &session->reorder_q);
 		spin_unlock(&session->reorder_q.lock);
-		pppol2tp_recv_dequeue_skb(session, skb);
-		spin_lock(&session->reorder_q.lock);
+		pppol2tp_recv_requeue_skb(session, skb);
+		goto again;
 	}
 
 out: