linux-kernel - Re: [BUG] 2.6.38-rc2: Circular Locking Dependency

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Message-Id: <20110208.150411.102552333.davem@davemloft.net>
Date:	Tue, 08 Feb 2011 15:04:11 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	Knut_Petersen@...nline.de
Cc:	paulus@...ba.org, linux-kernel@...r.kernel.org,
	mostrows@...thlink.net, linux-ppp@...r.kernel.org,
	xiaosuo@...il.com, eric.dumazet@...il.com, ebiederm@...ssion.com
Subject: Re: [BUG] 2.6.38-rc2: Circular Locking Dependency

From: David Miller <davem@...emloft.net>
Date: Tue, 08 Feb 2011 00:07:21 -0800 (PST)

[ Eric B., CC:'ing you so that you are aware of the init network
  namespace leak that's fixed as a side effect of this change. ]

> From: Knut Petersen <Knut_Petersen@...nline.de>
> Date: Tue, 08 Feb 2011 08:51:22 +0100
> 
>> I bisected the problem with the following result:
>> 
>> aa9421041128abb4d269ee1dc502ff65fb3b7d69 is the first bad commit
>> commit aa9421041128abb4d269ee1dc502ff65fb3b7d69
>> Author: Changli Gao <xiaosuo@...il.com>
>> Date:   Sat Dec 4 02:31:41 2010 +0000
>> 
>>     net: init ingress queue
>> 
>>     The dev field of ingress queue is forgot to initialized, then NULL
>>     pointer dereference happens in qdisc_alloc().
>> 
>>     Move inits of tx queues to netif_alloc_netdev_queues().
>> 
>>     Signed-off-by: Changli Gao <xiaosuo@...il.com>
>>     Acked-by: Eric Dumazet <eric.dumazet@...il.com>
>>     Signed-off-by: David S. Miller <davem@...emloft.net>
>> 
>> :040000 040000 dcbb6ab41c4308cba1bc6823d200dcf92aa402d8
>> b5e190ec681d26ffe62d1d0214c4ef77b8034189 M      net
> 
> Indeed, this initialization is now too early for the sake
> of getting the lockdep bits right.  The problem is that at
> the point in which we call netif_alloc_netdev_queue() we
> haven't initialized dev->type yet, it is therefore always
> zero when we setup the lockdep class for ->_xmit_lock.

Ok, this should fix it, please test it out for me.

Thanks!

--------------------
net: Fix lockdep regression caused by initializing netdev queues too early.

In commit aa9421041128abb4d269ee1dc502ff65fb3b7d69 ("net: init ingress
queue") we moved the allocation and lock initialization of the queues
into alloc_netdev_mq() since register_netdevice() is way too late.

The problem is that dev->type is not setup until the setup()
callback is invoked by alloc_netdev_mq(), and the dev->type is
what determines the lockdep class to use for the locks in the
queues.

Fix this by doing the queue allocation after the setup() callback
runs.

This is safe because the setup() callback is not allowed to make any
state changes that need to be undone on error (memory allocations,
etc.).  It may, however, make state changes that are undone by
free_netdev() (such as netif_napi_add(), which is done by the
ipoib driver's setup routine).

The previous code also leaked a reference to the &init_net namespace
object on RX/TX queue allocation failures.

Signed-off-by: David S. Miller <davem@...emloft.net>
---
 net/core/dev.c |   27 ++++++++++++++++-----------
 1 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index b6d0bf8..8e726cb 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5660,30 +5660,35 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
 
 	dev_net_set(dev, &init_net);
 
+	dev->gso_max_size = GSO_MAX_SIZE;
+
+	INIT_LIST_HEAD(&dev->ethtool_ntuple_list.list);
+	dev->ethtool_ntuple_list.count = 0;
+	INIT_LIST_HEAD(&dev->napi_list);
+	INIT_LIST_HEAD(&dev->unreg_list);
+	INIT_LIST_HEAD(&dev->link_watch_list);
+	dev->priv_flags = IFF_XMIT_DST_RELEASE;
+	setup(dev);
+
 	dev->num_tx_queues = txqs;
 	dev->real_num_tx_queues = txqs;
 	if (netif_alloc_netdev_queues(dev))
-		goto free_pcpu;
+		goto free_all;
 
 #ifdef CONFIG_RPS
 	dev->num_rx_queues = rxqs;
 	dev->real_num_rx_queues = rxqs;
 	if (netif_alloc_rx_queues(dev))
-		goto free_pcpu;
+		goto free_all;
 #endif
 
-	dev->gso_max_size = GSO_MAX_SIZE;
-
-	INIT_LIST_HEAD(&dev->ethtool_ntuple_list.list);
-	dev->ethtool_ntuple_list.count = 0;
-	INIT_LIST_HEAD(&dev->napi_list);
-	INIT_LIST_HEAD(&dev->unreg_list);
-	INIT_LIST_HEAD(&dev->link_watch_list);
-	dev->priv_flags = IFF_XMIT_DST_RELEASE;
-	setup(dev);
 	strcpy(dev->name, name);
 	return dev;
 
+free_all:
+	free_netdev(dev);
+	return NULL;
+
 free_pcpu:
 	free_percpu(dev->pcpu_refcnt);
 	kfree(dev->_tx);
-- 
1.7.4

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