pkt_sched: gen_kill_estimator() rcu fixes

gen_kill_estimator() API is incomplete or not well documented, since
caller should make sure an RCU grace period is respected before
freeing stats_lock.

This was partially addressed in commit 5d944c640b
(gen_estimator: deadlock fix), but same problem exist for all
gen_kill_estimator() users, if lock they use is not already RCU
protected.

A code review shows xt_RATEEST.c, act_api.c, act_police.c have this
problem. Other are ok because they use qdisc lock, already RCU
protected.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/act_api.c

@@ -26,6 +26,11 @@
 #include <net/act_api.h>
 #include <net/netlink.h>
 
+static void tcf_common_free_rcu(struct rcu_head *head)
+{
+	kfree(container_of(head, struct tcf_common, tcfc_rcu));
+}
+
 void tcf_hash_destroy(struct tcf_common *p, struct tcf_hashinfo *hinfo)
 {
 	unsigned int h = tcf_hash(p->tcfc_index, hinfo->hmask);
@@ -38,7 +43,11 @@ void tcf_hash_destroy(struct tcf_common *p, struct tcf_hashinfo *hinfo)
 			write_unlock_bh(hinfo->lock);
 			gen_kill_estimator(&p->tcfc_bstats,
 					   &p->tcfc_rate_est);
-			kfree(p);
+			/*
+			 * gen_estimator est_timer() might access p->tcfc_lock
+			 * or bstats, wait a RCU grace period before freeing p
+			 */
+			call_rcu(&p->tcfc_rcu, tcf_common_free_rcu);
 			return;
 		}
 	}

net/sched/act_police.c

@@ -97,6 +97,11 @@ nla_put_failure:
 	goto done;
 }
 
+static void tcf_police_free_rcu(struct rcu_head *head)
+{
+	kfree(container_of(head, struct tcf_police, tcf_rcu));
+}
+
 static void tcf_police_destroy(struct tcf_police *p)
 {
 	unsigned int h = tcf_hash(p->tcf_index, POL_TAB_MASK);
@@ -113,7 +118,11 @@ static void tcf_police_destroy(struct tcf_police *p)
 				qdisc_put_rtab(p->tcfp_R_tab);
 			if (p->tcfp_P_tab)
 				qdisc_put_rtab(p->tcfp_P_tab);
-			kfree(p);
+			/*
+			 * gen_estimator est_timer() might access p->tcf_lock
+			 * or bstats, wait a RCU grace period before freeing p
+			 */
+			call_rcu(&p->tcf_rcu, tcf_police_free_rcu);
 			return;
 		}
 	}
@@ -397,6 +406,7 @@ static void __exit
 police_cleanup_module(void)
 {
 	tcf_unregister_action(&act_police_ops);
+	rcu_barrier(); /* Wait for completion of call_rcu()'s (tcf_police_free_rcu) */
 }
 
 module_init(police_init_module);