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Date:	Sat, 8 Mar 2008 11:43:22 +0100
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Denys Fedoryshchenko <denys@...p.net.lb>
Cc:	jamal <hadi@...erus.ca>, netdev@...r.kernel.org
Subject: Re: circular locking, mirred, 2.6.24.2

On Sat, Mar 08, 2008 at 12:16:52PM +0200, Denys Fedoryshchenko wrote:
> Update. I am not able to reproduce on my PC, but still able to reproduce on 
> PPPoE server (but here i cannot take risk to use 2.6.25-rcX kernels). This is 
> PPPoE:
> 
> [2148614.154684]
> [2148614.154688] =======================================================
> [2148614.154805] [ INFO: possible circular locking dependency detected ]
> [2148614.154862] 2.6.24.3-build-0023 #9
> [2148614.154913] -------------------------------------------------------
> [2148614.154969] swapper/0 is trying to acquire lock:
> [2148614.155023]  (&ifb_queue_lock_key){-+..}, at: [<c0289d4d>] 
> dev_queue_xmit+0x177/0x302
> [2148614.155245]
> [2148614.155246] but task is already holding lock:
> [2148614.155346]  (&p->tcfc_lock){-+..}, at: [<f8a10066>] tcf_mirred+0x20/
> 0x180 [act_mirred]
> [2148614.155569]
> [2148614.155570] which lock already depends on the new lock.


...Hmm... the same day I sent to you "take 2" of my patch which was more
complete (lockdep_set_class for ingress_lock added). Could you try this?
It still could be not enough, and something similar is needed for
tcfc_lock in act_mirred, but I'd like to see a report after this patch
first.

As Jamal wrote this all is a false-positive with ifb, but I think it's
needed to please lockdep.

Thanks,
Jarek P.

PS: I resend this "take 2" here:
---

 drivers/net/ifb.c |   24 ++++++++++++++++++++++++
 1 files changed, 24 insertions(+), 0 deletions(-)

diff --git a/drivers/net/ifb.c b/drivers/net/ifb.c
index 15949d3..c553b62 100644
--- a/drivers/net/ifb.c
+++ b/drivers/net/ifb.c
@@ -227,6 +227,27 @@ static struct rtnl_link_ops ifb_link_ops __read_mostly = {
 module_param(numifbs, int, 0);
 MODULE_PARM_DESC(numifbs, "Number of ifb devices");
 
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+/*
+ * dev_ifb->queue_lock is usually taken after dev->ingress_lock,
+ * reversely to e.g. qdisc_lock_tree(). It should be safe until
+ * ifb doesn't take dev->queue_lock with dev_ifb->ingress_lock.
+ * But lockdep should know that ifb has different locks from dev.
+ */
+static struct lock_class_key ifb_queue_lock_key;
+static struct lock_class_key ifb_ingress_lock_key;
+
+static inline void ifb_set_lock_classes(struct net_device *dev_ifb)
+{
+	lockdep_set_class(&dev_ifb->queue_lock, &ifb_queue_lock_key);
+	lockdep_set_class(&dev_ifb->ingress_lock, &ifb_ingress_lock_key);
+}
+#else
+static inline void ifb_set_lock_classes(struct net_device *dev_ifb)
+{
+}
+#endif	/* CONFIG_DEBUG_LOCK_ALLOC */
+
 static int __init ifb_init_one(int index)
 {
 	struct net_device *dev_ifb;
@@ -246,6 +267,9 @@ static int __init ifb_init_one(int index)
 	err = register_netdevice(dev_ifb);
 	if (err < 0)
 		goto err;
+
+	ifb_set_lock_classes(dev_ifb);
+
 	return 0;
 
 err:
--
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