net: sched: cls_u32: Undo refcount decrement in case update failed

In the case of an update, when TCA_U32_LINK is set, u32_set_parms will
decrement the refcount of the ht_down (struct tc_u_hnode) pointer
present in the older u32 filter which we are replacing. However, if
u32_replace_hw_knode errors out, the update command fails and that
ht_down pointer continues decremented. To fix that, when
u32_replace_hw_knode fails, check if ht_down's refcount was decremented
and undo the decrement.

Fixes: d34e3e181395 ("net: cls_u32: Add support for skip-sw flag to tc u32 classifier.")
Signed-off-by: Victor Nogueira <[e-mail]>
Acked-by: Jamal Hadi Salim <[e-mail]>
Reviewed-by: Pedro Tammela <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/sched/cls_u32.c

···
 		if (err) {
 			u32_unbind_filter(tp, new, tb);
 
+			if (tb[TCA_U32_LINK]) {
+				struct tc_u_hnode *ht_old;
+
+				ht_old = rtnl_dereference(n->ht_down);
+				if (ht_old)
+					ht_old->refcnt++;
+			}
 			__u32_destroy_key(new);
 			return err;
 		}