bonding: Fix deadlock in bonding driver resulting from internal locking when using netpoll

The monitoring paths in the bonding driver take write locks that are shared by
the tx path.  If netconsole is in use, these paths can call printk which puts us
in the netpoll tx path, which, if netconsole is attached to the bonding driver,
result in deadlock (the xmit_lock guards are useless in netpoll_send_skb, as the
monitor paths in the bonding driver don't claim the xmit_lock, nor should they).
The solution is to use a per cpu flag internal to the driver to indicate when a
cpu is holding the lock in a path that might recusrse into the tx path for the
driver via netconsole.  By checking this flag on transmit, we can defer the
sending of the netconsole frames until a later time using the retransmit feature
of netpoll_send_skb that is triggered on the return code NETDEV_TX_BUSY.  I've
tested this and am able to transmit via netconsole while causing failover
conditions on the bond slave links.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 30 insertions, 0 deletions

diff --git a/drivers/net/bonding/bonding.h b/drivers/net/bonding/bonding.h
index c15f21347486..2c12a5f812f4 100644
--- a/drivers/net/bonding/bonding.h
+++ b/drivers/net/bonding/bonding.h
@@ -19,6 +19,7 @@
 #include <linux/proc_fs.h>
 #include <linux/if_bonding.h>
 #include <linux/kobject.h>
+#include <linux/cpumask.h>
 #include <linux/in6.h>
 #include "bond_3ad.h"
 #include "bond_alb.h"
@@ -117,6 +118,35 @@
                 bond_for_each_slave_from(bond, pos, cnt, (bond)->first_slave)
 
 
+#ifdef CONFIG_NET_POLL_CONTROLLER
+extern cpumask_var_t netpoll_block_tx;
+
+static inline void block_netpoll_tx(void)
+{
+        preempt_disable();
+        BUG_ON(cpumask_test_and_set_cpu(smp_processor_id(),
+                                        netpoll_block_tx));
+}
+
+static inline void unblock_netpoll_tx(void)
+{
+        BUG_ON(!cpumask_test_and_clear_cpu(smp_processor_id(),
+                                           netpoll_block_tx));
+        preempt_enable();
+}
+
+static inline int is_netpoll_tx_blocked(struct net_device *dev)
+{
+        if (unlikely(dev->priv_flags & IFF_IN_NETPOLL))
+                return cpumask_test_cpu(smp_processor_id(), netpoll_block_tx);
+        return 0;
+}
+#else
+#define block_netpoll_tx()
+#define unblock_netpoll_tx()
+#define is_netpoll_tx_blocked(dev) (0)
+#endif
+
 struct bond_params {
         int mode;
         int xmit_policy;