net: get rid of rtable->idev

It seems idev field in struct rtable has no special purpose, but adding
extra atomic ops.

We hold refcounts on the device itself (using percpu data, so pretty
cheap in current kernel).

infiniband case is solved using dst.dev instead of idev->dev

Removal of this field means routing without route cache is now using
shared data, percpu data, and only potential contention is a pair of
atomic ops on struct neighbour per forwarded packet.

About 5% speedup on routing test.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Roland Dreier <rolandd@cisco.com>
Cc: Sean Hefty <sean.hefty@intel.com>
Cc: Hal Rosenstock <hal.rosenstock@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/xfrm4_policy.c

@@ -80,10 +80,6 @@ static int xfrm4_fill_dst(struct xfrm_dst *xdst, struct net_device *dev,
 	xdst->u.dst.dev = dev;
 	dev_hold(dev);
 
-	xdst->u.rt.idev = in_dev_get(dev);
-	if (!xdst->u.rt.idev)
-		return -ENODEV;
-
 	xdst->u.rt.peer = rt->peer;
 	if (rt->peer)
 		atomic_inc(&rt->peer->refcnt);
@@ -189,8 +185,6 @@ static void xfrm4_dst_destroy(struct dst_entry *dst)
 {
 	struct xfrm_dst *xdst = (struct xfrm_dst *)dst;
 
-	if (likely(xdst->u.rt.idev))
-		in_dev_put(xdst->u.rt.idev);
 	if (likely(xdst->u.rt.peer))
 		inet_putpeer(xdst->u.rt.peer);
 	xfrm_dst_destroy(xdst);
@@ -199,27 +193,9 @@ static void xfrm4_dst_destroy(struct dst_entry *dst)
 static void xfrm4_dst_ifdown(struct dst_entry *dst, struct net_device *dev,
 			     int unregister)
 {
-	struct xfrm_dst *xdst;
-
 	if (!unregister)
 		return;
 
-	xdst = (struct xfrm_dst *)dst;
-	if (xdst->u.rt.idev->dev == dev) {
-		struct in_device *loopback_idev =
-			in_dev_get(dev_net(dev)->loopback_dev);
-		BUG_ON(!loopback_idev);
-
-		do {
-			in_dev_put(xdst->u.rt.idev);
-			xdst->u.rt.idev = loopback_idev;
-			in_dev_hold(loopback_idev);
-			xdst = (struct xfrm_dst *)xdst->u.dst.child;
-		} while (xdst->u.dst.xfrm);
-
-		__in_dev_put(loopback_idev);
-	}
-
 	xfrm_dst_ifdown(dst, dev);
 }