[NETPOLL]: allow multiple netpoll_clients to register against one interface

This patch provides support for registering multiple netpoll clients to the
same network device.  Only one of these clients may register an rx_hook,
however.  In practice, this restriction has not been problematic.  It is
worth mentioning, though, that the current design can be easily extended to
allow for the registration of multiple rx_hooks.

The basic idea of the patch is that the rx_np pointer in the netpoll_info
structure points to the struct netpoll that has rx_hook filled in.  Aside
from this one case, there is no need for a pointer from the struct
net_device to an individual struct netpoll.

A lock is introduced to protect the setting and clearing of the np_rx
pointer.  The pointer will only be cleared upon netpoll client module
removal, and the lock should be uncontested.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 41 insertions, 13 deletions

diff --git a/include/linux/netpoll.h b/include/linux/netpoll.h
index 388cd91bc7a6..bcd0ac33f592 100644
--- a/include/linux/netpoll.h
+++ b/include/linux/netpoll.h
@@ -27,7 +27,8 @@ struct netpoll_info {
         spinlock_t poll_lock;
         int poll_owner;
         int rx_flags;
-        struct netpoll *np;
+        spinlock_t rx_lock;
+        struct netpoll *rx_np; /* netpoll that registered an rx_hook */
 };
 
 void netpoll_poll(struct netpoll *np);
@@ -44,11 +45,19 @@ void netpoll_queue(struct sk_buff *skb);
 static inline int netpoll_rx(struct sk_buff *skb)
 {
         struct netpoll_info *npinfo = skb->dev->npinfo;
+        unsigned long flags;
+        int ret = 0;
 
-        if (!npinfo || !npinfo->rx_flags)
+        if (!npinfo || (!npinfo->rx_np && !npinfo->rx_flags))
                 return 0;
 
-        return npinfo->np && __netpoll_rx(skb);
+        spin_lock_irqsave(&npinfo->rx_lock, flags);
+        /* check rx_flags again with the lock held */
+        if (npinfo->rx_flags && __netpoll_rx(skb))
+                ret = 1;
+        spin_unlock_irqrestore(&npinfo->rx_lock, flags);
+
+        return ret;
 }
 
 static inline void netpoll_poll_lock(struct net_device *dev)
diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index ab3c0c9713b0..c327c9edadc5 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -349,11 +349,15 @@ static void arp_reply(struct sk_buff *skb)
         unsigned char *arp_ptr;
         int size, type = ARPOP_REPLY, ptype = ETH_P_ARP;
         u32 sip, tip;
+        unsigned long flags;
         struct sk_buff *send_skb;
         struct netpoll *np = NULL;
 
-        if (npinfo)
-                np = npinfo->np;
+        spin_lock_irqsave(&npinfo->rx_lock, flags);
+        if (npinfo->rx_np && npinfo->rx_np->dev == skb->dev)
+                np = npinfo->rx_np;
+        spin_unlock_irqrestore(&npinfo->rx_lock, flags);
+
         if (!np)
                 return;
 
@@ -436,9 +440,9 @@ int __netpoll_rx(struct sk_buff *skb)
         int proto, len, ulen;
         struct iphdr *iph;
         struct udphdr *uh;
-        struct netpoll *np = skb->dev->npinfo->np;
+        struct netpoll *np = skb->dev->npinfo->rx_np;
 
-        if (!np->rx_hook)
+        if (!np)
                 goto out;
         if (skb->dev->type != ARPHRD_ETHER)
                 goto out;
@@ -619,6 +623,7 @@ int netpoll_setup(struct netpoll *np)
         struct net_device *ndev = NULL;
         struct in_device *in_dev;
         struct netpoll_info *npinfo;
+        unsigned long flags;
 
         if (np->dev_name)
                 ndev = dev_get_by_name(np->dev_name);
@@ -634,9 +639,10 @@ int netpoll_setup(struct netpoll *np)
                 if (!npinfo)
                         goto release;
 
-                npinfo->np = NULL;
+                npinfo->rx_np = NULL;
                 npinfo->poll_lock = SPIN_LOCK_UNLOCKED;
                 npinfo->poll_owner = -1;
+                npinfo->rx_lock = SPIN_LOCK_UNLOCKED;
         } else
                 npinfo = ndev->npinfo;
 
@@ -706,9 +712,13 @@ int netpoll_setup(struct netpoll *np)
                        np->name, HIPQUAD(np->local_ip));
         }
 
-        if(np->rx_hook)
-                npinfo->rx_flags = NETPOLL_RX_ENABLED;
-        npinfo->np = np;
+        if (np->rx_hook) {
+                spin_lock_irqsave(&npinfo->rx_lock, flags);
+                npinfo->rx_flags |= NETPOLL_RX_ENABLED;
+                npinfo->rx_np = np;
+                spin_unlock_irqrestore(&npinfo->rx_lock, flags);
+        }
+        /* last thing to do is link it to the net device structure */
         ndev->npinfo = npinfo;
 
         return 0;
@@ -723,11 +733,20 @@ int netpoll_setup(struct netpoll *np)
 
 void netpoll_cleanup(struct netpoll *np)
 {
+        struct netpoll_info *npinfo;
+        unsigned long flags;
+
         if (np->dev) {
-                if (np->dev->npinfo)
-                        np->dev->npinfo->np = NULL;
+                npinfo = np->dev->npinfo;
+                if (npinfo && npinfo->rx_np == np) {
+                        spin_lock_irqsave(&npinfo->rx_lock, flags);
+                        npinfo->rx_np = NULL;
+                        npinfo->rx_flags &= ~NETPOLL_RX_ENABLED;
+                        spin_unlock_irqrestore(&npinfo->rx_lock, flags);
+                }
                 dev_put(np->dev);
         }
+
         np->dev = NULL;
 }