diff mbox series

[net-next,06/12] net: sched: flower: handle concurrent mask insertion

Message ID 20190214074712.17846-7-vladbu@mellanox.com
State Changes Requested
Delegated to: David Miller
Headers show
Series Refactor flower classifier to remove dependency on rtnl lock | expand

Commit Message

Vlad Buslov Feb. 14, 2019, 7:47 a.m. UTC 
Without rtnl lock protection masks with same key can be inserted
concurrently. Insert temporary mask with reference count zero to masks
hashtable. This will cause any concurrent modifications to retry.

Wait for rcu grace period to complete after removing temporary mask from
masks hashtable to accommodate concurrent readers.

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Suggested-by: Jiri Pirko <jiri@mellanox.com>
---
 net/sched/cls_flower.c | 41 ++++++++++++++++++++++++++++++++++-------
 1 file changed, 34 insertions(+), 7 deletions(-)

Comments

Stefano Brivio Feb. 15, 2019, 10:46 p.m. UTC | #1 
On Thu, 14 Feb 2019 09:47:06 +0200
Vlad Buslov <vladbu@mellanox.com> wrote:

> @@ -1327,19 +1330,36 @@ static int fl_check_assign_mask(struct cls_fl_head *head,
>  	int ret = 0;
>  
>  	rcu_read_lock();
> -	fnew->mask = rhashtable_lookup_fast(&head->ht, mask, mask_ht_params);
> +
> +	/* Insert mask as temporary node to prevent concurrent creation of mask
> +	 * with same key. Any concurrent lookups with same key will return
> +	 * EAGAIN because mask's refcnt is zero. It is safe to insert

Nit: -EAGAIN
diff mbox series

Patch

diff --git a/net/sched/cls_flower.c b/net/sched/cls_flower.c
index b41b72e894a6..2b032303f8d5 100644
--- a/net/sched/cls_flower.c
+++ b/net/sched/cls_flower.c
@@ -1301,11 +1301,14 @@  static struct fl_flow_mask *fl_create_new_mask(struct cls_fl_head *head,
 	INIT_LIST_HEAD_RCU(&newmask->filters);
 
 	refcount_set(&newmask->refcnt, 1);
-	err = rhashtable_insert_fast(&head->ht, &newmask->ht_node,
-				     mask_ht_params);
+	err = rhashtable_replace_fast(&head->ht, &mask->ht_node,
+				      &newmask->ht_node, mask_ht_params);
 	if (err)
 		goto errout_destroy;
 
+	/* Wait until any potential concurrent users of mask are finished */
+	synchronize_rcu();
+
 	list_add_tail_rcu(&newmask->list, &head->masks);
 
 	return newmask;
@@ -1327,19 +1330,36 @@  static int fl_check_assign_mask(struct cls_fl_head *head,
 	int ret = 0;
 
 	rcu_read_lock();
-	fnew->mask = rhashtable_lookup_fast(&head->ht, mask, mask_ht_params);
+
+	/* Insert mask as temporary node to prevent concurrent creation of mask
+	 * with same key. Any concurrent lookups with same key will return
+	 * EAGAIN because mask's refcnt is zero. It is safe to insert
+	 * stack-allocated 'mask' to masks hash table because we call
+	 * synchronize_rcu() before returning from this function (either in case
+	 * of error or after replacing it with heap-allocated mask in
+	 * fl_create_new_mask()).
+	 */
+	fnew->mask = rhashtable_lookup_get_insert_fast(&head->ht,
+						       &mask->ht_node,
+						       mask_ht_params);
 	if (!fnew->mask) {
 		rcu_read_unlock();
 
-		if (fold)
-			return -EINVAL;
+		if (fold) {
+			ret = -EINVAL;
+			goto errout_cleanup;
+		}
 
 		newmask = fl_create_new_mask(head, mask);
-		if (IS_ERR(newmask))
-			return PTR_ERR(newmask);
+		if (IS_ERR(newmask)) {
+			ret = PTR_ERR(newmask);
+			goto errout_cleanup;
+		}
 
 		fnew->mask = newmask;
 		return 0;
+	} else if (IS_ERR(fnew->mask)) {
+		ret = PTR_ERR(fnew->mask);
 	} else if (fold && fold->mask != fnew->mask) {
 		ret = -EINVAL;
 	} else if (!refcount_inc_not_zero(&fnew->mask->refcnt)) {
@@ -1348,6 +1368,13 @@  static int fl_check_assign_mask(struct cls_fl_head *head,
 	}
 	rcu_read_unlock();
 	return ret;
+
+errout_cleanup:
+	rhashtable_remove_fast(&head->ht, &mask->ht_node,
+			       mask_ht_params);
+	/* Wait until any potential concurrent users of mask are finished */
+	synchronize_rcu();
+	return ret;
 }
 
 static int fl_set_parms(struct net *net, struct tcf_proto *tp,