[PATCH 2.6.35] bonding: prevent netpoll over bonded interfaces

[PATCH 2.6.35] bonding: prevent netpoll over bonded interfaces

[Andy Gospodarek]

Support for netpoll over bonded interfaces was added here:

	commit f6dc31a85cd46a959bdd987adad14c3b645e03c1
	Author: WANG Cong <amwang@redhat.com>
	Date:   Thu May 6 00:48:51 2010 -0700

	    bonding: make bonding support netpoll

but it is bad enough that we should probably just disable netpoll over
bonding until some of the locking logic in the bonding driver is changed
or converted completely to RCU.  Simple actions like changing the active
slave in active-backup mode will hang the box if a high enough printk
debugging level is enabled.

Keeping the old code around will be good for anyone that wants to work
on it (and for after the RCU conversion), so I propose this small patch
rather than ripping it all out.

Signed-off-by: Andy Gospodarek <andy@greyhouse.net>

---
 drivers/net/bonding/bond_main.c |   33 ++++++++++++++++++++++-----------
 1 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 5e12462..c3d98dd 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -168,7 +168,7 @@ static int arp_ip_count;
 static int bond_mode	= BOND_MODE_ROUNDROBIN;
 static int xmit_hashtype = BOND_XMIT_POLICY_LAYER2;
 static int lacp_fast;
-
+static int disable_netpoll = 1;
 
 const struct bond_parm_tbl bond_lacp_tbl[] = {
 {	"slow",		AD_LACP_SLOW},
@@ -1742,15 +1742,23 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev)
 	bond_set_carrier(bond);
 
 #ifdef CONFIG_NET_POLL_CONTROLLER
-	if (slaves_support_netpoll(bond_dev)) {
-		bond_dev->priv_flags &= ~IFF_DISABLE_NETPOLL;
-		if (bond_dev->npinfo)
-			slave_dev->npinfo = bond_dev->npinfo;
-	} else if (!(bond_dev->priv_flags & IFF_DISABLE_NETPOLL)) {
+	/*
+	 * Netpoll and bonding is broken, make sure it is not initialized
+	 * until it is fixed.
+	 */
+	if (disable_netpoll) {
 		bond_dev->priv_flags |= IFF_DISABLE_NETPOLL;
-		pr_info("New slave device %s does not support netpoll\n",
-			slave_dev->name);
-		pr_info("Disabling netpoll support for %s\n", bond_dev->name);
+	} else {
+		if (slaves_support_netpoll(bond_dev)) {
+			bond_dev->priv_flags &= ~IFF_DISABLE_NETPOLL;
+			if (bond_dev->npinfo)
+				slave_dev->npinfo = bond_dev->npinfo;
+		} else if (!(bond_dev->priv_flags & IFF_DISABLE_NETPOLL)) {
+			bond_dev->priv_flags |= IFF_DISABLE_NETPOLL;
+			pr_info("New slave device %s does not support netpoll\n",
+				slave_dev->name);
+			pr_info("Disabling netpoll support for %s\n", bond_dev->name);
+		}
 	}
 #endif
 	read_unlock(&bond->lock);
@@ -1950,8 +1958,11 @@ int bond_release(struct net_device *bond_dev, struct net_device *slave_dev)
 
 #ifdef CONFIG_NET_POLL_CONTROLLER
 	read_lock_bh(&bond->lock);
-	if (slaves_support_netpoll(bond_dev))
-		bond_dev->priv_flags &= ~IFF_DISABLE_NETPOLL;
+
+	 /* Make sure netpoll over stays disabled until fixed. */
+	if (!disable_netpoll)
+		if (slaves_support_netpoll(bond_dev))
+				bond_dev->priv_flags &= ~IFF_DISABLE_NETPOLL;
 	read_unlock_bh(&bond->lock);
 	if (slave_dev->netdev_ops->ndo_netpoll_cleanup)
 		slave_dev->netdev_ops->ndo_netpoll_cleanup(slave_dev);

Re: [PATCH 2.6.35] bonding: prevent netpoll over bonded interfaces

[Andi Kleen]

Andy Gospodarek <andy@greyhouse.net> writes:

> Support for netpoll over bonded interfaces was added here:
>
> 	commit f6dc31a85cd46a959bdd987adad14c3b645e03c1
> 	Author: WANG Cong <amwang@redhat.com>
> 	Date:   Thu May 6 00:48:51 2010 -0700
>
> 	    bonding: make bonding support netpoll
>
> but it is bad enough that we should probably just disable netpoll over
> bonding until some of the locking logic in the bonding driver is changed
> or converted completely to RCU.  Simple actions like changing the active
> slave in active-backup mode will hang the box if a high enough printk
> debugging level is enabled.

Normally you just need to prevent the printks when called from poll
context. That's not rocket science.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only.

Re: [PATCH 2.6.35] bonding: prevent netpoll over bonded interfaces

[Jay Vosburgh]

Andi Kleen <andi@firstfloor.org> wrote:

>Andy Gospodarek <andy@greyhouse.net> writes:
>
>> Support for netpoll over bonded interfaces was added here:
>>
>> 	commit f6dc31a85cd46a959bdd987adad14c3b645e03c1
>> 	Author: WANG Cong <amwang@redhat.com>
>> 	Date:   Thu May 6 00:48:51 2010 -0700
>>
>> 	    bonding: make bonding support netpoll
>>
>> but it is bad enough that we should probably just disable netpoll over
>> bonding until some of the locking logic in the bonding driver is changed
>> or converted completely to RCU.  Simple actions like changing the active
>> slave in active-backup mode will hang the box if a high enough printk
>> debugging level is enabled.
>
>Normally you just need to prevent the printks when called from poll
>context. That's not rocket science.

	The problem with bonding is that its own printks will come back
into bonding via netpoll and deadlock in various ways.  Without re-doing
the locking, the fix would really be to make every printk in bonding
happen without holding any locks.  Converting the driver to RCU is
probably the only way to resolve this, and that's at least verging on
rocket science.

	I'm in favor of the patch; netpoll over bonding is sufficiently
unstable that I'm comfortable requiring that it be explicitly enabled by
the user.  I'd also be comfortable with a patch that removes netpoll for
bonding, but I don't mind leaving the netpoll stuff there for use by
those who want to live dangerously.

Signed-off-by: Jay Vosburgh <fubar@us.ibm.com>


	-J

---
	-Jay Vosburgh, IBM Linux Technology Center, fubar@us.ibm.com

Re: [PATCH 2.6.35] bonding: prevent netpoll over bonded interfaces

[David Miller]

From: Andy Gospodarek <andy@greyhouse.net>
Date: Fri, 25 Jun 2010 15:50:44 -0400

> 
> Support for netpoll over bonded interfaces was added here:
> 
> 	commit f6dc31a85cd46a959bdd987adad14c3b645e03c1
> 	Author: WANG Cong <amwang@redhat.com>
> 	Date:   Thu May 6 00:48:51 2010 -0700
> 
> 	    bonding: make bonding support netpoll
> 
> but it is bad enough that we should probably just disable netpoll over
> bonding until some of the locking logic in the bonding driver is changed
> or converted completely to RCU.  Simple actions like changing the active
> slave in active-backup mode will hang the box if a high enough printk
> debugging level is enabled.
> 
> Keeping the old code around will be good for anyone that wants to work
> on it (and for after the RCU conversion), so I propose this small patch
> rather than ripping it all out.
> 
> Signed-off-by: Andy Gospodarek <andy@greyhouse.net>

Applied, thanks a lot Andy.