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 5d944c640b4
(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>

1 files changed, 11 insertions, 1 deletions

diff --git a/net/netfilter/xt_RATEEST.c b/net/netfilter/xt_RATEEST.c
index 69c01e10f8af..de079abd5bc8 100644
--- a/net/netfilter/xt_RATEEST.c
+++ b/net/netfilter/xt_RATEEST.c
@@ -60,13 +60,22 @@ struct xt_rateest *xt_rateest_lookup(const char *name)
 }
 EXPORT_SYMBOL_GPL(xt_rateest_lookup);
 
+static void xt_rateest_free_rcu(struct rcu_head *head)
+{
+        kfree(container_of(head, struct xt_rateest, rcu));
+}
+
 void xt_rateest_put(struct xt_rateest *est)
 {
         mutex_lock(&xt_rateest_mutex);
         if (--est->refcnt == 0) {
                 hlist_del(&est->list);
                 gen_kill_estimator(&est->bstats, &est->rstats);
-                kfree(est);
+                /*
+                 * gen_estimator est_timer() might access est->lock or bstats,
+                 * wait a RCU grace period before freeing 'est'
+                 */
+                call_rcu(&est->rcu, xt_rateest_free_rcu);
         }
         mutex_unlock(&xt_rateest_mutex);
 }
@@ -179,6 +188,7 @@ static int __init xt_rateest_tg_init(void)
 static void __exit xt_rateest_tg_fini(void)
 {
         xt_unregister_target(&xt_rateest_tg_reg);
+        rcu_barrier(); /* Wait for completion of call_rcu()'s (xt_rateest_free_rcu) */
 }