1 files changed, 43 insertions, 22 deletions

diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index 6611f292b6cb..076d5cdde656 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -816,6 +816,9 @@ EXPORT_SYMBOL(tcf_idr_cleanup);
  * its reference and bind counters, and return 1. Otherwise insert temporary
  * error pointer (to prevent concurrent users from inserting actions with same
  * index) and return 0.
+ *
+ * May return -EAGAIN for binding actions in case of a parallel add/delete on
+ * the requested index.
  */
 
 int tcf_idr_check_alloc(struct tc_action_net *tn, u32 *index,
@@ -824,43 +827,61 @@ int tcf_idr_check_alloc(struct tc_action_net *tn, u32 *index,
 	struct tcf_idrinfo *idrinfo = tn->idrinfo;
 	struct tc_action *p;
 	int ret;
+	u32 max;
 
-again:
-	mutex_lock(&idrinfo->lock);
 	if (*index) {
+again:
+		rcu_read_lock();
 		p = idr_find(&idrinfo->action_idr, *index);
+
 		if (IS_ERR(p)) {
 			/* This means that another process allocated
 			 * index but did not assign the pointer yet.
 			 */
-			mutex_unlock(&idrinfo->lock);
+			rcu_read_unlock();
 			goto again;
 		}
 
-		if (p) {
-			refcount_inc(&p->tcfa_refcnt);
-			if (bind)
-				atomic_inc(&p->tcfa_bindcnt);
-			*a = p;
-			ret = 1;
-		} else {
-			*a = NULL;
-			ret = idr_alloc_u32(&idrinfo->action_idr, NULL, index,
-					    *index, GFP_KERNEL);
-			if (!ret)
-				idr_replace(&idrinfo->action_idr,
-					    ERR_PTR(-EBUSY), *index);
+		if (!p) {
+			/* Empty slot, try to allocate it */
+			max = *index;
+			rcu_read_unlock();
+			goto new;
+		}
+
+		if (!refcount_inc_not_zero(&p->tcfa_refcnt)) {
+			/* Action was deleted in parallel */
+			rcu_read_unlock();
+			return -EAGAIN;
 		}
+
+		if (bind)
+			atomic_inc(&p->tcfa_bindcnt);
+		*a = p;
+
+		rcu_read_unlock();
+
+		return 1;
 	} else {
+		/* Find a slot */
 		*index = 1;
-		*a = NULL;
-		ret = idr_alloc_u32(&idrinfo->action_idr, NULL, index,
-				    UINT_MAX, GFP_KERNEL);
-		if (!ret)
-			idr_replace(&idrinfo->action_idr, ERR_PTR(-EBUSY),
-				    *index);
+		max = UINT_MAX;
 	}
+
+new:
+	*a = NULL;
+
+	mutex_lock(&idrinfo->lock);
+	ret = idr_alloc_u32(&idrinfo->action_idr, ERR_PTR(-EBUSY), index, max,
+			    GFP_KERNEL);
 	mutex_unlock(&idrinfo->lock);
+
+	/* N binds raced for action allocation,
+	 * retry for all the ones that failed.
+	 */
+	if (ret == -ENOSPC && *index == max)
+		ret = -EAGAIN;
+
 	return ret;
 }
 EXPORT_SYMBOL(tcf_idr_check_alloc);