Revert "ipv6: Handle race in addrconf_dad_work"

This reverts commit a3ce2a21.

Eric reported tests failings with commit. After digging into it,
the bottom line is that the DAD sequence is not to be messed with.
There are too many cases that are expected to proceed regardless
of whether a device is up.

Revert the patch and I will send a different solution for the
problem Rajendra reported.
Signed-off-by: David Ahern <dsahern@gmail.com>
Cc: Eric Dumazet <edumazet@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -4032,12 +4032,6 @@ static void addrconf_dad_work(struct work_struct *w)
 
 	rtnl_lock();
 
-	/* check if device was taken down before this delayed work
-	 * function could be canceled
-	 */
-	if (idev->dead || !(idev->if_flags & IF_READY))
-		goto out;
-
 	spin_lock_bh(&ifp->lock);
 	if (ifp->state == INET6_IFADDR_STATE_PREDAD) {
 		action = DAD_BEGIN;
@@ -4083,6 +4077,11 @@ static void addrconf_dad_work(struct work_struct *w)
 		goto out;
 
 	write_lock_bh(&idev->lock);
+	if (idev->dead || !(idev->if_flags & IF_READY)) {
+		write_unlock_bh(&idev->lock);
+		goto out;
+	}
+
 	spin_lock(&ifp->lock);
 	if (ifp->state == INET6_IFADDR_STATE_DEAD) {
 		spin_unlock(&ifp->lock);